diff --git a/balancer.go b/balancer.go
index 9fade63..154cde0 100644
--- a/balancer.go
+++ b/balancer.go
@@ -71,100 +71,185 @@ func (n *Notification) success(current map[string][]int32) *Notification {
 
 // --------------------------------------------------------------------
 
-type balancer struct {
-	client    sarama.Client
-	memberIDs []string
-	topics    map[string]*topicInfo
-}
+// Assignor is a function which returns specific partition assignments
+// given the set of topic subscriptions of a given group.
+type Assignor func(subs *Subscriptions, topics []*TopicPartitions) Assignments
 
-type topicInfo struct {
+// TopicPartitions identifies a topic and its partition IDs.
+type TopicPartitions struct {
+	Name       string
 	Partitions []int32
-	MemberIDs  []string
+}
+
+// Subscriptions contains information about all members in a consumer
+// group, and which topics they have subscribed to.
+type Subscriptions struct {
+	memberIDs   []string
+	subscribers map[string][]string
+}
+
+// NewSubscriptions returns an empty set of subscriptions.
+func NewSubscriptions() *Subscriptions {
+	return &Subscriptions{
+		memberIDs:   []string{},
+		subscribers: map[string][]string{},
+	}
+}
+
+// Members returns the list of all member IDs in the group.
+func (m *Subscriptions) Members() []string {
+	return m.memberIDs
+}
+
+// AddSubscriber registers a member as subscribed to a topic.
+// Returns self.
+func (m *Subscriptions) AddSubscriber(memberID, topic string) *Subscriptions {
+	seen := false
+	for i := range m.memberIDs {
+		if m.memberIDs[i] == memberID {
+			seen = true
+		}
+	}
+
+	if !seen {
+		m.memberIDs = append(m.memberIDs, memberID)
+	}
+
+	m.subscribers[topic] = append(m.subscribers[topic], memberID)
+	return m
+}
+
+// SubscribedMembers returns the full list of members subscribed
+// to a topic.
+func (m *Subscriptions) SubscribedMembers(topic string) []string {
+	return m.subscribers[topic]
+}
+
+// IsSubscribed returns true if a member is subscribed to a topic.
+func (m *Subscriptions) IsSubscribed(memberID, topic string) bool {
+	subs, ok := m.subscribers[topic]
+	if !ok {
+		return false
+	}
+
+	for i := range subs {
+		if subs[i] == memberID {
+			return true
+		}
+	}
+
+	return false
+}
+
+// Assignments is a mapping of member IDs to the topic partitions that they
+// have been assigned.
+type Assignments map[string]map[string][]int32
+
+// NewAssignments returns an empty set of assignments.
+func NewAssignments() Assignments {
+	return map[string]map[string][]int32{}
+}
+
+// Assign adds a partition to the list of a member's assignments.
+func (a Assignments) Assign(memberID, topic string, partition int32) {
+	topics, ok := a[memberID]
+	if !ok {
+		topics = map[string][]int32{}
+		a[memberID] = topics
+	}
+
+	topics[topic] = append(topics[topic], partition)
+}
+
+type balancer struct {
+	client sarama.Client
+	subs   *Subscriptions
+	topics []*TopicPartitions
 }
 
 func newBalancerFromMeta(client sarama.Client, members map[string]sarama.ConsumerGroupMemberMetadata) (*balancer, error) {
 	balancer := &balancer{
-		client:    client,
-		memberIDs: make([]string, 0, len(members)),
-		topics:    make(map[string]*topicInfo),
+		client: client,
+		subs:   NewSubscriptions(),
+		topics: []*TopicPartitions{},
 	}
+
 	for memberID, meta := range members {
-		balancer.memberIDs = append(balancer.memberIDs, memberID)
 		for _, topic := range meta.Topics {
-			if err := balancer.Topic(memberID, topic); err != nil {
+			balancer.subs.AddSubscriber(memberID, topic)
+			if err := balancer.AddTopic(topic); err != nil {
 				return nil, err
 			}
 		}
 	}
 
-	sort.Strings(balancer.memberIDs)
 	return balancer, nil
 }
 
-func (r *balancer) Topic(memberID string, name string) error {
-	info, ok := r.topics[name]
-	if !ok {
-		nums, err := r.client.Partitions(name)
-		if err != nil {
-			return err
-		}
-
-		r.topics[name] = &topicInfo{
-			MemberIDs:  []string{memberID},
-			Partitions: nums,
+func (r *balancer) AddTopic(name string) error {
+	for i := range r.topics {
+		if r.topics[i].Name == name {
+			return nil
 		}
+	}
 
-		return nil
+	nums, err := r.client.Partitions(name)
+	if err != nil {
+		return err
 	}
 
-	info.MemberIDs = append(info.MemberIDs, memberID)
+	r.topics = append(r.topics, &TopicPartitions{
+		Name:       name,
+		Partitions: nums,
+	})
 	return nil
 }
 
-func (r *balancer) Perform(s Strategy) map[string]map[string][]int32 {
+func (r *balancer) Perform(fn Assignor) Assignments {
 	if r == nil {
 		return nil
 	}
 
-	switch s {
-	case StrategyRoundRobin:
-		return assignRoundRobin(r.memberIDs, r.topics)
-	default:
-		return assignRange(r.memberIDs, r.topics)
-	}
+	return fn(r.subs, r.topics)
 }
 
-func assignRange(_ []string, topics map[string]*topicInfo) map[string]map[string][]int32 {
-	tlen := len(topics)
-	res := make(map[string]map[string][]int32)
-
-	for topic, info := range topics {
-		mlen := len(info.MemberIDs)
-		plen := len(info.Partitions)
-
-		sort.Strings(info.MemberIDs)
-		for pos, memberID := range info.MemberIDs {
+// RangeAssignor assigns partitions to subscribed group members by
+// dividing the number of partitions, per-topic, by the number of
+// consumers to determine the number of partitions per consumer that
+// should be assigned. If the value does not evenly divide, consumers
+// lexicographically earlier will be assigned an extra partition.
+func RangeAssignor(subs *Subscriptions, topics []*TopicPartitions) Assignments {
+	assignments := NewAssignments()
+
+	sort.Slice(topics, func(i, j int) bool { return topics[i].Name < topics[j].Name })
+	for _, tp := range topics {
+		members := subs.SubscribedMembers(tp.Name)
+		mlen := len(members)
+		plen := len(tp.Partitions)
+
+		sort.Strings(members)
+		for pos, memberID := range members {
 			n, i := float64(plen)/float64(mlen), float64(pos)
 			min := int(math.Floor(i*n + 0.5))
 			max := int(math.Floor((i+1)*n + 0.5))
-			sub := info.Partitions[min:max]
-			if len(sub) <= 0 {
-				continue
+			sub := tp.Partitions[min:max]
+			for i := range sub {
+				assignments.Assign(memberID, tp.Name, sub[i])
 			}
-
-			assigned, ok := res[memberID]
-			if !ok {
-				assigned = make(map[string][]int32, tlen)
-				res[memberID] = assigned
-			}
-			assigned[topic] = sub
 		}
 	}
 
-	return res
+	return assignments
 }
 
-func assignRoundRobin(memberIDs []string, topics map[string]*topicInfo) map[string]map[string][]int32 {
+// RoundRobinAssignor assigns partitions by iterating through the
+// list of group members and assigning one to each consumer until
+// all partitions have been assigned. If a group member is not
+// subscribed to a topic, the next subscribed member is assigned
+// instead.
+func RoundRobinAssignor(subs *Subscriptions, topics []*TopicPartitions) Assignments {
+	assignments := NewAssignments()
+	memberIDs := subs.Members()
 	sort.Strings(memberIDs)
 
 	r := ring.New(len(memberIDs))
@@ -173,40 +258,22 @@ func assignRoundRobin(memberIDs []string, topics map[string]*topicInfo) map[stri
 		r = r.Next()
 	}
 
-	isSubscribed := func(memberID string, topic string) bool {
-		info, ok := topics[topic]
-		if !ok {
-			return false
-		}
-
-		for _, subscriber := range info.MemberIDs {
-			if memberID == subscriber {
-				return true
-			}
+	sort.Slice(topics, func(i, j int) bool { return topics[i].Name < topics[j].Name })
+	for _, tp := range topics {
+		if len(subs.SubscribedMembers(tp.Name)) == 0 {
+			continue
 		}
 
-		return false
-	}
-
-	tlen := len(topics)
-	res := make(map[string]map[string][]int32, r.Len())
-
-	for topic, info := range topics {
-		for i := range info.Partitions {
-			for ; !isSubscribed(r.Value.(string), topic); r = r.Next() {
+		partitions := tp.Partitions
+		for i := range partitions {
+			for ; !subs.IsSubscribed(r.Value.(string), tp.Name); r = r.Next() {
 				continue
 			}
 
-			memberID := r.Value.(string)
-			assigned, ok := res[memberID]
-			if !ok {
-				assigned = make(map[string][]int32, tlen)
-				res[memberID] = assigned
-			}
-			assigned[topic] = append(assigned[topic], info.Partitions[i])
+			assignments.Assign(r.Value.(string), tp.Name, partitions[i])
 			r = r.Next()
 		}
 	}
 
-	return res
+	return assignments
 }
diff --git a/balancer_test.go b/balancer_test.go
index 4a88be8..a650927 100644
--- a/balancer_test.go
+++ b/balancer_test.go
@@ -55,237 +55,205 @@ var _ = Describe("balancer", func() {
 		Expect(err).NotTo(HaveOccurred())
 	})
 
-	It("should parse from meta data", func() {
-		Expect(subject.memberIDs).To(Equal([]string{"a", "b"}))
+	It("should track topic partitions", func() {
 		Expect(subject.topics).To(HaveLen(3))
 	})
 
-})
+	It("should track group member subscriptions", func() {
+		subs := subject.subs
+		Expect(subs.Members()).To(ConsistOf([]string{"a", "b"}))
+		Expect(subs.SubscribedMembers("one")).To(ConsistOf([]string{"a", "b"}))
+		Expect(subs.SubscribedMembers("two")).To(Equal([]string{"a"}))
+		Expect(subs.SubscribedMembers("three")).To(Equal([]string{"b"}))
+	})
 
-var _ = Describe("partition assignment", func() {
+})
 
-	DescribeTable("Ranges",
-		func(memberIDs []string, topics map[string]*topicInfo, expected map[string]map[string][]int32) {
-			assignments := assignRange(memberIDs, topics)
-			Expect(assignments).To(Equal(expected))
+var _ = Describe("Assignors", func() {
+	DescribeTable("Range",
+		func(subs submap, topics topicparts, expected Assignments) {
+			result := RangeAssignor(subs.Subscriptions(), topics.TopicPartitions())
+			Expect(result).To(Equal(expected))
 		},
 
-		Entry("three members, three partitions", []string{"M1", "M2", "M3"}, map[string]*topicInfo{
-			"t1": &topicInfo{
-				Partitions: []int32{0, 1, 2},
-				MemberIDs:  []string{"M1", "M2", "M3"},
-			},
-		}, map[string]map[string][]int32{
-			"M1": {"t1": {0}},
-			"M2": {"t1": {1}},
-			"M3": {"t1": {2}},
+		Entry("one consumer, no topics", submap{"m0": {"t0"}}, topicparts{}, Assignments{}),
+		Entry("one consumer, no such topic", submap{"m0": {"t1"}}, topicparts{"t0": {0}}, Assignments{}),
+
+		Entry("one consumer, one topic", submap{"m0": {"t0"}}, topicparts{"t0": {0, 1, 2}}, Assignments{
+			"m0": {"t0": {0, 1, 2}},
 		}),
 
-		Entry("member ID order", []string{"M3", "M1", "M2"}, map[string]*topicInfo{
-			"t1": &topicInfo{
-				Partitions: []int32{0, 1, 2},
-				MemberIDs:  []string{"M1", "M2", "M3"},
-			},
-		}, map[string]map[string][]int32{
-			"M1": {"t1": {0}},
-			"M2": {"t1": {1}},
-			"M3": {"t1": {2}},
+		Entry("one consumer, two topics, one subscribed", submap{"m0": {"t0"}}, topicparts{
+			"t0": {0, 1, 2},
+			"t1": {0, 1, 2},
+		}, Assignments{
+			"m0": {"t0": {0, 1, 2}},
 		}),
 
-		Entry("more members than partitions", []string{"M1", "M2", "M3"}, map[string]*topicInfo{
-			"t1": &topicInfo{
-				Partitions: []int32{0, 1},
-				MemberIDs:  []string{"M1", "M2", "M3"},
-			},
-		}, map[string]map[string][]int32{
-			"M1": {"t1": {0}},
-			"M3": {"t1": {1}},
+		Entry("one consumer, multiple topics", submap{"m0": {"t0", "t1"}}, topicparts{
+			"t0": {0, 1, 2},
+			"t1": {0, 1, 2},
+		}, Assignments{
+			"m0": {"t0": {0, 1, 2}, "t1": {0, 1, 2}},
 		}),
 
-		Entry("far more members than partitions", []string{"M1", "M2", "M3"}, map[string]*topicInfo{
-			"t1": &topicInfo{
-				Partitions: []int32{0},
-				MemberIDs:  []string{"M1", "M2", "M3"},
-			},
-		}, map[string]map[string][]int32{
-			"M2": {"t1": {0}},
+		Entry("two consumers, one topic, one partition", submap{
+			"m0": {"t0"},
+			"m1": {"t0"},
+		}, topicparts{
+			"t0": {0},
+		}, Assignments{
+			"m0": {"t0": {0}},
 		}),
 
-		Entry("fewer members than partitions", []string{"M1", "M2", "M3"}, map[string]*topicInfo{
-			"t1": &topicInfo{
-				Partitions: []int32{0, 1, 2, 3},
-				MemberIDs:  []string{"M1", "M2", "M3"},
-			},
-		}, map[string]map[string][]int32{
-			"M1": {"t1": {0}},
-			"M2": {"t1": {1, 2}},
-			"M3": {"t1": {3}},
+		Entry("two consumers, one topic, two partitions", submap{
+			"m0": {"t0"},
+			"m1": {"t0"},
+		}, topicparts{
+			"t0": {0, 1},
+		}, Assignments{
+			"m0": {"t0": {0}},
+			"m1": {"t0": {1}},
 		}),
 
-		Entry("uneven members/partitions ratio", []string{"M1", "M2", "M3"}, map[string]*topicInfo{
-			"t1": &topicInfo{
-				Partitions: []int32{0, 2, 4, 6, 8},
-				MemberIDs:  []string{"M1", "M2", "M3"},
-			},
-		}, map[string]map[string][]int32{
-			"M1": {"t1": {0, 2}},
-			"M2": {"t1": {4}},
-			"M3": {"t1": {6, 8}},
+		Entry("multiple consumers, mixed topics", submap{
+			"m0": {"t0"},
+			"m1": {"t0", "t1"},
+			"m2": {"t0"},
+		}, topicparts{
+			"t0": {0, 1, 2},
+			"t1": {0, 1},
+		}, Assignments{
+			"m0": {"t0": {0}},
+			"m1": {"t0": {1}, "t1": {0, 1}},
+			"m2": {"t0": {2}},
 		}),
 
-		Entry("multiple topics", []string{"M1", "M2", "M3"}, map[string]*topicInfo{
-			"t1": &topicInfo{
-				Partitions: []int32{0, 1, 2},
-				MemberIDs:  []string{"M1", "M2", "M3"},
-			},
-			"t2": &topicInfo{
-				Partitions: []int32{0, 1},
-				MemberIDs:  []string{"M1", "M2", "M3"},
-			},
-			"t3": &topicInfo{
-				Partitions: []int32{0},
-				MemberIDs:  []string{"M1", "M2", "M3"},
-			},
-		}, map[string]map[string][]int32{
-			"M1": {"t1": {0}, "t2": {0}},
-			"M2": {"t1": {1}, "t3": {0}},
-			"M3": {"t1": {2}, "t2": {1}},
+		Entry("two consumers, two topics, six partitions", submap{
+			"m0": {"t0", "t1"},
+			"m1": {"t0", "t1"},
+		}, topicparts{
+			"t0": {0, 1, 2},
+			"t1": {0, 1, 2},
+		}, Assignments{
+			"m0": {"t0": {0, 1}, "t1": {0, 1}},
+			"m1": {"t0": {2}, "t1": {2}},
 		}),
 
-		Entry("different subscriptions", []string{"M1", "M2", "M3"}, map[string]*topicInfo{
-			"t1": &topicInfo{
-				Partitions: []int32{0, 1, 2},
-				MemberIDs:  []string{"M1", "M2", "M3"},
-			},
-			"t2": &topicInfo{
-				Partitions: []int32{0, 1},
-				MemberIDs:  []string{"M2", "M3"},
-			},
-			"t3": &topicInfo{
-				Partitions: []int32{0},
-				MemberIDs:  []string{"M1"},
-			},
-		}, map[string]map[string][]int32{
-			"M1": {"t1": {0}, "t3": {0}},
-			"M2": {"t1": {1}, "t2": {0}},
-			"M3": {"t1": {2}, "t2": {1}},
+		Entry("heavily uneven partition counts", submap{
+			"m0": {"t0", "t1", "t2"},
+			"m1": {"t0", "t1", "t2"},
+		}, topicparts{
+			"t0": {0, 1, 2, 3, 4},
+			"t1": {0, 1},
+			"t2": {0},
+		}, Assignments{
+			"m0": {"t0": {0, 1, 2}, "t1": {0}, "t2": {0}},
+			"m1": {"t0": {3, 4}, "t1": {1}},
 		}),
 	)
 
 	DescribeTable("RoundRobin",
-		func(memberIDs []string, topics map[string]*topicInfo, expected map[string]map[string][]int32) {
-			assignments := assignRoundRobin(memberIDs, topics)
-			Expect(assignments).To(Equal(expected))
+		func(subs submap, topics topicparts, expected Assignments) {
+			result := RoundRobinAssignor(subs.Subscriptions(), topics.TopicPartitions())
+			Expect(result).To(Equal(expected))
 		},
 
-		Entry("three members, three partitions", []string{"M1", "M2", "M3"}, map[string]*topicInfo{
-			"t1": &topicInfo{
-				Partitions: []int32{0, 1, 2},
-				MemberIDs:  []string{"M1", "M2", "M3"},
-			},
-		}, map[string]map[string][]int32{
-			"M1": {"t1": {0}},
-			"M2": {"t1": {1}},
-			"M3": {"t1": {2}},
+		Entry("one consumer, no topics", submap{"m0": {"t0"}}, topicparts{}, Assignments{}),
+		Entry("one consumer, no such topic", submap{"m0": {"t1"}}, topicparts{"t0": {0}}, Assignments{}),
+
+		Entry("one consumer, one topic", submap{"m0": {"t0"}}, topicparts{"t0": {0, 1, 2}}, Assignments{
+			"m0": {"t0": {0, 1, 2}},
 		}),
 
-		Entry("member ID order", []string{"M3", "M1", "M2"}, map[string]*topicInfo{
-			"t1": &topicInfo{
-				Partitions: []int32{0, 1, 2},
-				MemberIDs:  []string{"M1", "M2", "M3"},
-			},
-		}, map[string]map[string][]int32{
-			"M1": {"t1": {0}},
-			"M2": {"t1": {1}},
-			"M3": {"t1": {2}},
+		Entry("one consumer, two topics, one subscribed", submap{"m0": {"t0"}}, topicparts{
+			"t0": {0, 1, 2},
+			"t1": {0, 1, 2},
+		}, Assignments{
+			"m0": {"t0": {0, 1, 2}},
 		}),
 
-		Entry("more members than partitions", []string{"M1", "M2", "M3"}, map[string]*topicInfo{
-			"t1": &topicInfo{
-				Partitions: []int32{0, 1},
-				MemberIDs:  []string{"M1", "M2", "M3"},
-			},
-		}, map[string]map[string][]int32{
-			"M1": {"t1": {0}},
-			"M2": {"t1": {1}},
+		Entry("one consumer, multiple topics", submap{"m0": {"t0", "t1"}}, topicparts{
+			"t0": {0, 1, 2},
+			"t1": {0, 1, 2},
+		}, Assignments{
+			"m0": {"t0": {0, 1, 2}, "t1": {0, 1, 2}},
 		}),
 
-		Entry("far more members than partitions", []string{"M1", "M2", "M3"}, map[string]*topicInfo{
-			"t1": &topicInfo{
-				Partitions: []int32{0},
-				MemberIDs:  []string{"M1", "M2", "M3"},
-			},
-		}, map[string]map[string][]int32{
-			"M1": {"t1": {0}},
+		Entry("two consumers, one topic, two partitions", submap{
+			"m0": {"t0"},
+			"m1": {"t0"},
+		}, topicparts{
+			"t0": {0, 1},
+		}, Assignments{
+			"m0": {"t0": {0}},
+			"m1": {"t0": {1}},
 		}),
 
-		Entry("fewer members than partitions", []string{"M1", "M2", "M3"}, map[string]*topicInfo{
-			"t1": &topicInfo{
-				Partitions: []int32{0, 1, 2, 3},
-				MemberIDs:  []string{"M1", "M2", "M3"},
-			},
-		}, map[string]map[string][]int32{
-			"M1": {"t1": {0, 3}},
-			"M2": {"t1": {1}},
-			"M3": {"t1": {2}},
+		Entry("two consumers, one topic, one partition", submap{
+			"m0": {"t0"},
+			"m1": {"t0"},
+		}, topicparts{
+			"t0": {0},
+		}, Assignments{
+			"m0": {"t0": {0}},
 		}),
 
-		Entry("uneven members/partitions ratio", []string{"M1", "M2", "M3"}, map[string]*topicInfo{
-			"t1": &topicInfo{
-				Partitions: []int32{0, 2, 4, 6, 8},
-				MemberIDs:  []string{"M1", "M2", "M3"},
-			},
-		}, map[string]map[string][]int32{
-			"M1": {"t1": {0, 6}},
-			"M2": {"t1": {2, 8}},
-			"M3": {"t1": {4}},
+		Entry("multiple consumers, mixed topics", submap{
+			"m0": {"t0"},
+			"m1": {"t0", "t1"},
+			"m2": {"t0"},
+		}, topicparts{
+			"t0": {0, 1, 2},
+			"t1": {0, 1},
+		}, Assignments{
+			"m0": {"t0": {0}},
+			"m1": {"t0": {1}, "t1": {0, 1}},
+			"m2": {"t0": {2}},
 		}),
 
-		Entry("multiple topics", []string{"M1", "M2"}, map[string]*topicInfo{
-			"t1": &topicInfo{
-				Partitions: []int32{0, 1, 2},
-				MemberIDs:  []string{"M1", "M2"},
-			},
-			"t2": &topicInfo{
-				Partitions: []int32{0, 1, 2},
-				MemberIDs:  []string{"M1", "M2"},
-			},
-		}, map[string]map[string][]int32{
-			"M1": {
-				"t1": {0, 2},
-				"t2": {1},
-			},
-			"M2": {
-				"t1": {1},
-				"t2": {0, 2},
-			},
+		Entry("two consumers, two topics, six partitions", submap{
+			"m0": {"t0", "t1"},
+			"m1": {"t0", "t1"},
+		}, topicparts{
+			"t0": {0, 1, 2},
+			"t1": {0, 1, 2},
+		}, Assignments{
+			"m0": {"t0": {0, 2}, "t1": {1}},
+			"m1": {"t0": {1}, "t1": {0, 2}},
 		}),
 
-		Entry("different subscriptions", []string{"M1", "M2", "M3"}, map[string]*topicInfo{
-			"t1": &topicInfo{
-				Partitions: []int32{0},
-				MemberIDs:  []string{"M1", "M2", "M3"},
-			},
-			"t2": &topicInfo{
-				Partitions: []int32{0, 1},
-				MemberIDs:  []string{"M2", "M3"},
-			},
-			"t3": &topicInfo{
-				Partitions: []int32{0, 1, 2},
-				MemberIDs:  []string{"M3"},
-			},
-		}, map[string]map[string][]int32{
-			"M1": {
-				"t1": {0},
-			},
-			"M2": {
-				"t2": {0},
-			},
-			"M3": {
-				"t2": {1},
-				"t3": {0, 1, 2},
-			},
+		Entry("heavily uneven partition counts", submap{
+			"m0": {"t0", "t1", "t2"},
+			"m1": {"t0", "t1", "t2"},
+		}, topicparts{
+			"t0": {0, 1, 2, 3, 4},
+			"t1": {0, 1},
+			"t2": {0},
+		}, Assignments{
+			"m0": {"t0": {0, 2, 4}, "t1": {1}},
+			"m1": {"t0": {1, 3}, "t1": {0}, "t2": {0}},
 		}),
 	)
-
 })
+
+type submap map[string][]string
+type topicparts map[string][]int32
+
+func (s submap) Subscriptions() *Subscriptions {
+	subs := NewSubscriptions()
+	for memberID, topics := range s {
+		for _, topic := range topics {
+			subs.AddSubscriber(memberID, topic)
+		}
+	}
+	return subs
+}
+
+func (t topicparts) TopicPartitions() []*TopicPartitions {
+	tps := []*TopicPartitions{}
+	for topic, partitions := range t {
+		tps = append(tps, &TopicPartitions{Name: topic, Partitions: partitions})
+	}
+	return tps
+}
diff --git a/config.go b/config.go
index 084b835..205d8a2 100644
--- a/config.go
+++ b/config.go
@@ -23,7 +23,12 @@ type Config struct {
 	// Group is the namespace for group management properties
 	Group struct {
 
-		// The strategy to use for the allocation of partitions to consumers (defaults to StrategyRange)
+		// The assignor implementation to use for the allocation of partitions to consumers.
+		// Defaults to RangeAssignor.
+		PartitionAssignor Assignor
+
+		// The strategy to use for the allocation of partitions to consumers. Defaults to
+		// StrategyRange. If PartitionAssignor is set, it takes precedence over this option.
 		PartitionStrategy Strategy
 
 		// By default, messages and errors from the subscribed topics and partitions are all multiplexed and
diff --git a/consumer.go b/consumer.go
index 13500cc..8b1adf3 100644
--- a/consumer.go
+++ b/consumer.go
@@ -706,7 +706,17 @@ func (c *Consumer) syncGroup(strategy *balancer) (map[string][]int32, error) {
 		GenerationId: generationID,
 	}
 
-	for memberID, topics := range strategy.Perform(c.client.config.Group.PartitionStrategy) {
+	assignor := c.client.config.Group.PartitionAssignor
+	if assignor == nil {
+		switch c.client.config.Group.PartitionStrategy {
+		case StrategyRoundRobin:
+			assignor = RoundRobinAssignor
+		default:
+			assignor = RangeAssignor
+		}
+	}
+
+	for memberID, topics := range strategy.Perform(assignor) {
 		if err := req.AddGroupAssignmentMember(memberID, &sarama.ConsumerGroupMemberAssignment{
 			Version: 1,
 			Topics:  topics,