diff --git a/block.go b/block.go
index aa70017d9..cd2da7bfa 100644
--- a/block.go
+++ b/block.go
@@ -1,10 +1,6 @@
 package tsdb
 
-import (
-	"io"
-	"sort"
-	"unsafe"
-)
+import "sort"
 
 const (
 	magicIndex  = 0xCAFECAFE
@@ -12,7 +8,9 @@ const (
 )
 
 // Block handles reads against a block of time series data within a time window.
-type Block interface{}
+type Block interface {
+	Querier(mint, maxt int64) Querier
+}
 
 const (
 	flagNone = 0
@@ -22,9 +20,6 @@ const (
 // A skiplist maps offsets to values. The values found in the data at an
 // offset are strictly greater than the indexed value.
 type skiplist interface {
-	// A skiplist can serialize itself into a writer.
-	io.WriterTo
-
 	// offset returns the offset to data containing values of x and lower.
 	offset(x int64) (uint32, bool)
 }
@@ -48,16 +43,3 @@ func (sl simpleSkiplist) offset(x int64) (uint32, bool) {
 	}
 	return sl[i-1].offset, true
 }
-
-func (sl simpleSkiplist) WriteTo(w io.Writer) (n int64, err error) {
-	for _, s := range sl {
-		b := ((*[unsafe.Sizeof(skiplistPair{})]byte)(unsafe.Pointer(&s)))[:]
-
-		m, err := w.Write(b)
-		if err != nil {
-			return n + int64(m), err
-		}
-		n += int64(m)
-	}
-	return n, err
-}
diff --git a/db.go b/db.go
index c546a4cd3..103544d39 100644
--- a/db.go
+++ b/db.go
@@ -89,11 +89,6 @@ func (db *DB) Close() error {
 	return nil
 }
 
-// Querier returns a new querier over the database.
-func (db *DB) Querier(start, end int64) Querier {
-	return nil
-}
-
 // Appender adds a batch of samples.
 type Appender interface {
 	// Add adds a sample pair to the appended batch.
@@ -199,7 +194,7 @@ type SeriesShard struct {
 	logger    log.Logger
 
 	mtx    sync.RWMutex
-	blocks *Block
+	blocks []*Block
 	head   *HeadBlock
 }
 
@@ -257,6 +252,12 @@ func (s *SeriesShard) appendBatch(ts int64, samples []Sample) error {
 	return nil
 }
 
+// blocksForRange returns all blocks within the shard that may contain
+// data for the given time range.
+func (s *SeriesShard) blocksForRange(mint, maxt int64) (bs []Block) {
+	return nil
+}
+
 // TODO(fabxc): make configurable.
 const shardGracePeriod = 60 * 1000 // 60 seconds for millisecond scale
 
diff --git a/index.go b/index.go
index 7faf45af6..43bbd8ee0 100644
--- a/index.go
+++ b/index.go
@@ -83,16 +83,30 @@ func (p *memPostings) add(id uint32, terms ...term) {
 
 // Iterator provides iterative access over a postings list.
 type Iterator interface {
-	// Next advances the iterator and returns true if another
-	// value was found.
+	// Next advances the iterator and returns true if another value was found.
 	Next() bool
+
 	// Seek advances the iterator to value v or greater and returns
 	// true if a value was found.
 	Seek(v uint32) bool
+
 	// Value returns the value at the current iterator position.
 	Value() uint32
+
+	// Err returns the last error of the iterator.
+	Err() error
 }
 
+// errIterator is an empty iterator that always errors.
+type errIterator struct {
+	err error
+}
+
+func (e errIterator) Next() bool       { return false }
+func (e errIterator) Seek(uint32) bool { return false }
+func (e errIterator) Value() uint32    { return 0 }
+func (e errIterator) Err() error       { return e.err }
+
 // Intersect returns a new iterator over the intersection of the
 // input iterators.
 func Intersect(its ...Iterator) Iterator {
@@ -123,6 +137,10 @@ func (it *intersectIterator) Seek(id uint32) bool {
 	return false
 }
 
+func (it *intersectIterator) Err() error {
+	return nil
+}
+
 // Merge returns a new iterator over the union of the input iterators.
 func Merge(its ...Iterator) Iterator {
 	if len(its) == 0 {
@@ -152,6 +170,10 @@ func (it *mergeIterator) Seek(id uint32) bool {
 	return false
 }
 
+func (it *mergeIterator) Err() error {
+	return nil
+}
+
 // listIterator implements the Iterator interface over a plain list.
 type listIterator struct {
 	list []uint32
@@ -175,6 +197,10 @@ func (it *listIterator) Seek(x uint32) bool {
 	return it.idx < len(it.list)
 }
 
+func (it *listIterator) Err() error {
+	return nil
+}
+
 type stringset map[string]struct{}
 
 func (ss stringset) set(s string) {
diff --git a/querier.go b/querier.go
index 5cb6310dc..59b77095f 100644
--- a/querier.go
+++ b/querier.go
@@ -1,6 +1,10 @@
 package tsdb
 
-import "github.com/fabxc/tsdb/chunks"
+import (
+	"fmt"
+
+	"github.com/fabxc/tsdb/chunks"
+)
 
 // Matcher matches a string.
 type Matcher interface {
@@ -11,34 +15,260 @@ type Matcher interface {
 // Querier provides querying access over time series data of a fixed
 // time range.
 type Querier interface {
-	// Range returns the timestamp range of the Querier.
-	Range() (start, end int64)
-
 	// Iterator returns an interator over the inverted index that
 	// matches the key label by the constraints of Matcher.
 	Iterator(key string, m Matcher) Iterator
 
-	// Labels resolves a label reference into a set of labels.
-	Labels(ref LabelRefs) (Labels, error)
-
 	// Series returns series provided in the index iterator.
-	Series(Iterator) []Series
+	Series(Iterator) ([]Series, error)
 
 	// LabelValues returns all potential values for a label name.
-	LabelValues(string) []string
+	LabelValues(string) ([]string, error)
 	// LabelValuesFor returns all potential values for a label name.
 	// under the constraint of another label.
-	LabelValuesFor(string, Label) []string
+	LabelValuesFor(string, Label) ([]string, error)
 
 	// Close releases the resources of the Querier.
 	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() (Labels, error)
+	// 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, error)
+	Iterator() SeriesIterator
+}
+
+func inRange(x, mint, maxt int64) bool {
+	return x >= mint && x <= maxt
+}
+
+// querier merges query results from a set of shard querieres.
+type querier struct {
+	mint, maxt int64
+	shards     []Querier
+}
+
+// Querier returns a new querier over the database for the given
+// time range.
+func (db *DB) Querier(mint, maxt int64) Querier {
+	q := &querier{
+		mint: mint,
+		maxt: maxt,
+	}
+	for _, s := range db.shards {
+		q.shards = append(q.shards, s.Querier(mint, maxt))
+	}
+
+	return q
+}
+
+// SeriesSet contains a set of series.
+type SeriesSet interface {
+}
+
+func (q *querier) Select(key string, m Matcher) SeriesSet {
+	return nil
+}
+
+func (q *querier) Iterator(key string, m Matcher) Iterator {
+	return nil
+}
+
+func (q *querier) Series(Iterator) ([]Series, error) {
+	return nil, nil
+}
+
+func (q *querier) LabelValues(string) ([]string, error) {
+	return nil, nil
+}
+
+func (q *querier) LabelValuesFor(string, Label) ([]string, error) {
+	return nil, fmt.Errorf("not implemented")
+}
+
+func (q *querier) Close() error {
+	return nil
+}
+
+// shardQuerier aggregates querying results from time blocks within
+// a single shard.
+type shardQuerier struct {
+	blocks []Querier
+}
+
+// Querier returns a new querier over the data shard for the given
+// time range.
+func (s *SeriesShard) Querier(mint, maxt int64) Querier {
+	blocks := s.blocksForRange(mint, maxt)
+
+	sq := &shardQuerier{
+		blocks: make([]Querier, 0, len(blocks)),
+	}
+	for _, b := range blocks {
+		sq.blocks = append(sq.blocks, b.Querier(mint, maxt))
+	}
+
+	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
+
+	for _, s := range q.blocks {
+		rit = Merge(rit, s.Iterator(name, m))
+	}
+
+	return rit
+}
+
+func (q *shardQuerier) Series(it Iterator) ([]Series, error) {
+	// Dedulicate series as we stream through the iterator. See comment
+	// on the Iterator method.
+
+	var series []Series
+	// var prev Labels
+
+	// 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 *shardQuerier) LabelValues(string) ([]string, error) {
+	return nil, nil
+}
+
+func (q *shardQuerier) LabelValuesFor(string, Label) ([]string, error) {
+	return nil, fmt.Errorf("not implemented")
+}
+
+func (q *shardQuerier) Close() error {
+	return nil
+}
+
+// blockQuerier provides querying access to a single block database.
+type blockQuerier struct {
+	mint, maxt int64
+
+	index  IndexReader
+	series SeriesReader
+}
+
+func newBlockQuerier(ix IndexReader, s SeriesReader, mint, maxt int64) *blockQuerier {
+	return &blockQuerier{
+		mint:   mint,
+		maxt:   maxt,
+		index:  ix,
+		series: s,
+	}
+}
+
+func (q *blockQuerier) Iterator(name string, m Matcher) Iterator {
+	tpls, err := q.index.LabelValues(name)
+	if err != nil {
+		return errIterator{err: err}
+	}
+	// TODO(fabxc): use interface upgrading to provide fast solution
+	// for equality and prefix matches. Tuples are lexicographically sorted.
+	var res []string
+
+	for i := 0; i < tpls.Len(); i++ {
+		vals, err := tpls.At(i)
+		if err != nil {
+			return errIterator{err: err}
+		}
+		if m.Match(vals[0]) {
+			res = append(res, vals[0])
+		}
+	}
+
+	var rit Iterator
+
+	for _, v := range res {
+		it, err := q.index.Postings(name, v)
+		if err != nil {
+			return errIterator{err: err}
+		}
+		rit = Intersect(rit, it)
+	}
+
+	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 {
+		return nil, err
+	}
+	res := make([]string, 0, tpls.Len())
+
+	for i := 0; i < tpls.Len(); i++ {
+		vals, err := tpls.At(i)
+		if err != nil {
+			return nil, err
+		}
+		res = append(res, vals[0])
+	}
+	return nil, nil
+}
+
+func (q *blockQuerier) LabelValuesFor(string, Label) ([]string, error) {
+	return nil, fmt.Errorf("not implemented")
+}
+
+func (q *blockQuerier) Close() error {
+	return nil
 }
 
 // SeriesIterator iterates over the data of a time series.
@@ -118,4 +348,17 @@ type bufferedSeriesIterator struct {
 	// the simpler interface.
 	//
 	// Consider making this the main external interface.
+	SeriesIterator
+
+	buf []sample // lookback buffer
+	i   int      // current head
+}
+
+type sample struct {
+	t int64
+	v float64
+}
+
+func (b *bufferedSeriesIterator) PeekBack(i int) (t int64, v float64, ok bool) {
+	return 0, 0, false
 }
diff --git a/reader.go b/reader.go
index ed7926c35..ab3621209 100644
--- a/reader.go
+++ b/reader.go
@@ -292,13 +292,14 @@ type series struct {
 	chunk   func(ref uint32) (chunks.Chunk, error)
 }
 
-func (s *series) Labels() (Labels, error) {
-	return s.labels, nil
+func (s *series) Labels() Labels {
+	return s.labels
 }
 
-func (s *series) Iterator() (SeriesIterator, error) {
-	// dereference skiplist and construct from chunk iterators.
-	return nil, nil
+func (s *series) Iterator() SeriesIterator {
+	var cs []chunks.Chunk
+
+	return newChunkSeriesIterator(cs)
 }
 
 type stringTuples struct {