diff --git a/db.go b/db.go
index 103544d390..78aa7ad84e 100644
--- a/db.go
+++ b/db.go
@@ -362,13 +362,6 @@ func (cd *chunkDesc) append(ts int64, v float64) (err error) {
 	return nil
 }
 
-// LabelRefs contains a reference to a label set that can be resolved
-// against a Querier.
-type LabelRefs struct {
-	block   uint64
-	offsets []uint32
-}
-
 // Label is a key/value pair of strings.
 type Label struct {
 	Name, Value string
diff --git a/querier.go b/querier.go
index 59b77095f0..ab8d95458b 100644
--- a/querier.go
+++ b/querier.go
@@ -2,25 +2,35 @@ package tsdb
 
 import (
 	"fmt"
+	"strings"
 
 	"github.com/fabxc/tsdb/chunks"
 )
 
 // Matcher matches a string.
 type Matcher interface {
+	Name() string
 	// Match returns true if the matcher applies to the string value.
 	Match(v string) bool
 }
 
+type equalMatcher struct {
+	name  string
+	value string
+}
+
+func MatchEquals(n, v string) Matcher {
+	return &equalMatcher{name: n, value: v}
+}
+
+func (m *equalMatcher) Name() string        { return m.name }
+func (m *equalMatcher) Match(v string) bool { return v == m.value }
+
 // Querier provides querying access over time series data of a fixed
 // time range.
 type Querier interface {
-	// Iterator returns an interator over the inverted index that
-	// matches the key label by the constraints of Matcher.
-	Iterator(key string, m Matcher) Iterator
-
-	// Series returns series provided in the index iterator.
-	Series(Iterator) ([]Series, error)
+	// Select returns a set of series that matches the given label matchers.
+	Select(...Matcher) SeriesSet
 
 	// LabelValues returns all potential values for a label name.
 	LabelValues(string) ([]string, error)
@@ -32,32 +42,14 @@ type Querier interface {
 	Close() error
 }
 
-func example(db *DB) error {
-	var m1, m2, m3, m4 Matcher
-
-	q := db.Querier(0, 1000)
-
-	series, err := q.Series(
-		Merge(
-			Intersect(q.Iterator("name", m1), q.Iterator("job", m2)),
-			Intersect(q.Iterator("name", m3), q.Iterator("job", m4)),
-		),
-	)
-	if err != nil {
-		return err
-	}
-	for _, s := range series {
-		s.Iterator()
-	}
-	return nil
-}
-
 // Series represents a single time series.
 type Series interface {
 	// Labels returns the complete set of labels identifying the series.
 	Labels() Labels
 	// Iterator returns a new iterator of the data of the series.
 	Iterator() SeriesIterator
+
+	// Ref() uint32
 }
 
 func inRange(x, mint, maxt int64) bool {
@@ -86,18 +78,20 @@ func (db *DB) Querier(mint, maxt int64) Querier {
 
 // SeriesSet contains a set of series.
 type SeriesSet interface {
+	Next() bool
+	Series() Series
+	Err() error
 }
 
-func (q *querier) Select(key string, m Matcher) SeriesSet {
-	return nil
-}
+func (q *querier) Select(ms ...Matcher) SeriesSet {
+	// We gather the non-overlapping series from every shard and simply
+	// return their union.
+	r := &mergedSeriesSet{}
 
-func (q *querier) Iterator(key string, m Matcher) Iterator {
-	return nil
-}
-
-func (q *querier) Series(Iterator) ([]Series, error) {
-	return nil, nil
+	for _, s := range q.shards {
+		r.sets = append(r.sets, s.Select(ms...))
+	}
+	return r
 }
 
 func (q *querier) LabelValues(string) ([]string, error) {
@@ -133,39 +127,139 @@ func (s *SeriesShard) Querier(mint, maxt int64) Querier {
 	return sq
 }
 
-func (q *shardQuerier) Iterator(name string, m Matcher) Iterator {
-	// Iterators from different blocks have no time overlap. The reference numbers
-	// they emit point to series sorted in lexicographic order.
-	// If actually retrieving an iterator result via the Series method, we can fully
-	// deduplicate series by simply comparing with the previous label set.
-	var rit Iterator
+type mergedSeriesSet struct {
+	sets []SeriesSet
 
-	for _, s := range q.blocks {
-		rit = Merge(rit, s.Iterator(name, m))
-	}
-
-	return rit
+	cur int
+	err error
 }
 
-func (q *shardQuerier) Series(it Iterator) ([]Series, error) {
-	// Dedulicate series as we stream through the iterator. See comment
-	// on the Iterator method.
+func (s *mergedSeriesSet) Series() Series { return s.sets[s.cur].Series() }
+func (s *mergedSeriesSet) Err() error     { return s.sets[s.cur].Err() }
 
-	var series []Series
-	// var prev Labels
+func (s *mergedSeriesSet) Next() bool {
+	// TODO(fabxc): We just emit the sets one after one. They are each
+	// lexicographically sorted. Should we emit their union sorted too?
+	if s.sets[s.cur].Next() {
+		return true
+	}
+	s.cur++
 
-	// for it.Next() {
-	// 	s, err := q.index.Series(it.Value())
-	// 	if err != nil {
-	// 		return nil, err
-	// 	}
-	// 	series = append(series, s)
-	// }
-	// if it.Err() != nil {
-	// 	return nil, it.Err()
-	// }
+	if s.cur == len(s.sets) {
+		return false
+	}
+	return s.Next()
+}
 
-	return series, nil
+type shardSeriesSet struct {
+	a, b SeriesSet
+
+	cur    Series
+	as, bs Series // peek ahead of each set
+}
+
+func newShardSeriesSet(a, b SeriesSet) *shardSeriesSet {
+	s := &shardSeriesSet{a: a, b: b}
+	// Initialize first elements of both sets as Next() needs
+	// one element look-ahead.
+	s.advanceA()
+	s.advanceB()
+
+	return s
+}
+
+// compareLabels compares the two label sets.
+// The result will be 0 if a==b, <0 if a < b, and >0 if a > b.
+func compareLabels(a, b Labels) int {
+	l := len(a)
+	if len(b) < l {
+		l = len(b)
+	}
+
+	for i := 0; i < l; i++ {
+		if d := strings.Compare(a[i].Name, b[i].Name); d != 0 {
+			return d
+		}
+	}
+	// If all labels so far were in common, the set with fewer labels comes first.
+	return len(b) - len(a)
+}
+
+func (s *shardSeriesSet) Series() Series {
+	return s.cur
+}
+
+func (s *shardSeriesSet) Err() error {
+	if s.a.Err() != nil {
+		return s.a.Err()
+	}
+	return s.b.Err()
+}
+
+func (s *shardSeriesSet) compare() int {
+	if s.as == nil {
+		return 1
+	}
+	if s.bs == nil {
+		return -1
+	}
+	return compareLabels(s.as.Labels(), s.bs.Labels())
+}
+
+func (s *shardSeriesSet) advanceA() {
+	if s.a.Next() {
+		s.as = s.a.Series()
+	} else {
+		s.as = nil
+	}
+}
+
+func (s *shardSeriesSet) advanceB() {
+	if s.b.Next() {
+		s.bs = s.b.Series()
+	} else {
+		s.bs = nil
+	}
+}
+
+func (s *shardSeriesSet) Next() bool {
+	if s.as == nil && s.bs == nil {
+		return false
+	}
+
+	d := s.compare()
+	// Both sets contain the current series. Chain them into a single one.
+	if d > 0 {
+		s.cur = s.bs
+		s.advanceB()
+
+	} else if d < 0 {
+		s.cur = s.as
+		s.advanceA()
+
+	} else {
+		s.cur = &chainedSeries{series: []Series{s.as, s.bs}}
+		s.advanceA()
+		s.advanceB()
+	}
+	return true
+}
+
+func (q *shardQuerier) Select(ms ...Matcher) SeriesSet {
+	// Sets from different blocks have no time overlap. The reference numbers
+	// they emit point to series sorted in lexicographic order.
+	// We can fully connect partial series by simply comparing with the previous
+	// label set.
+	if len(q.blocks) == 0 {
+		return nil
+	}
+	r := q.blocks[0].Select(ms...)
+
+	for _, s := range q.blocks[1:] {
+		r = &shardSeriesSet{a: r, b: s.Select(ms...)}
+	}
+
+	return r
 }
 
 func (q *shardQuerier) LabelValues(string) ([]string, error) {
@@ -182,10 +276,10 @@ func (q *shardQuerier) Close() error {
 
 // blockQuerier provides querying access to a single block database.
 type blockQuerier struct {
-	mint, maxt int64
-
 	index  IndexReader
 	series SeriesReader
+
+	mint, maxt int64
 }
 
 func newBlockQuerier(ix IndexReader, s SeriesReader, mint, maxt int64) *blockQuerier {
@@ -197,8 +291,22 @@ func newBlockQuerier(ix IndexReader, s SeriesReader, mint, maxt int64) *blockQue
 	}
 }
 
-func (q *blockQuerier) Iterator(name string, m Matcher) Iterator {
-	tpls, err := q.index.LabelValues(name)
+func (q *blockQuerier) Select(ms ...Matcher) SeriesSet {
+	var its []Iterator
+	for _, m := range ms {
+		its = append(its, q.selectSingle(m))
+	}
+
+	// TODO(fabxc): pass down time range so the series iterator
+	// can be instantiated with it?
+	return &blockSeriesSet{
+		index: q.index,
+		it:    Intersect(its...),
+	}
+}
+
+func (q *blockQuerier) selectSingle(m Matcher) Iterator {
+	tpls, err := q.index.LabelValues(m.Name())
 	if err != nil {
 		return errIterator{err: err}
 	}
@@ -219,7 +327,7 @@ func (q *blockQuerier) Iterator(name string, m Matcher) Iterator {
 	var rit Iterator
 
 	for _, v := range res {
-		it, err := q.index.Postings(name, v)
+		it, err := q.index.Postings(m.Name(), v)
 		if err != nil {
 			return errIterator{err: err}
 		}
@@ -229,23 +337,6 @@ func (q *blockQuerier) Iterator(name string, m Matcher) Iterator {
 	return rit
 }
 
-func (q *blockQuerier) Series(it Iterator) ([]Series, error) {
-	var series []Series
-
-	for it.Next() {
-		s, err := q.index.Series(it.Value())
-		if err != nil {
-			return nil, err
-		}
-		series = append(series, s)
-	}
-	if it.Err() != nil {
-		return nil, it.Err()
-	}
-
-	return series, nil
-}
-
 func (q *blockQuerier) LabelValues(name string) ([]string, error) {
 	tpls, err := q.index.LabelValues(name)
 	if err != nil {
@@ -271,6 +362,36 @@ func (q *blockQuerier) Close() error {
 	return nil
 }
 
+// blockSeriesSet is a set of series from an inverted index query.
+type blockSeriesSet struct {
+	index IndexReader
+	it    Iterator
+
+	err error
+	cur Series
+}
+
+func (s *blockSeriesSet) Next() bool {
+	// Get next reference from postings iterator.
+	if !s.it.Next() {
+		s.err = s.it.Err()
+		return false
+	}
+
+	// Resolve reference to series.
+	series, err := s.index.Series(s.it.Value())
+	if err != nil {
+		s.err = err
+		return false
+	}
+
+	s.cur = series
+	return true
+}
+
+func (s *blockSeriesSet) Series() Series { return s.cur }
+func (s *blockSeriesSet) Err() error     { return s.err }
+
 // SeriesIterator iterates over the data of a time series.
 type SeriesIterator interface {
 	// Seek advances the iterator forward to the given timestamp.
@@ -285,6 +406,46 @@ type SeriesIterator interface {
 	Err() error
 }
 
+type chainedSeries struct {
+	series []Series
+}
+
+func (s *chainedSeries) Labels() Labels {
+	return s.series[0].Labels()
+}
+
+func (s *chainedSeries) Iterator() SeriesIterator {
+	it := &chainedSeriesIterator{
+		series: make([]SeriesIterator, 0, len(s.series)),
+	}
+	for _, series := range s.series {
+		it.series = append(it.series, series.Iterator())
+	}
+	return it
+}
+
+// chainedSeriesIterator implements a series iterater over a list
+// of time-sorted, non-overlapping chunks.
+type chainedSeriesIterator struct {
+	series []SeriesIterator
+}
+
+func (it *chainedSeriesIterator) Seek(t int64) bool {
+	return false
+}
+
+func (it *chainedSeriesIterator) Values() (t int64, v float64) {
+	return 0, 0
+}
+
+func (it *chainedSeriesIterator) Next() bool {
+	return false
+}
+
+func (it *chainedSeriesIterator) Err() error {
+	return nil
+}
+
 // chunkSeriesIterator implements a series iterator on top
 // of a list of time-sorted, non-overlapping chunks.
 type chunkSeriesIterator struct {