diff --git a/Makefile b/Makefile
index 4be0b733..9e7e1d24 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
 GOVERSION=$(shell go version | awk '{print $$3;}')
-PACKAGES=database deb files http utils
-ALL_PACKAGES=aptly cmd console database deb files http utils
+PACKAGES=database deb files http query utils
+ALL_PACKAGES=aptly cmd console database deb files http query utils
 BINPATH=$(abspath ./_vendor/bin)
 GOM_ENVIRONMENT=-test
 PYTHON?=python
diff --git a/query/lex.go b/query/lex.go
new file mode 100644
index 00000000..dc95d8d9
--- /dev/null
+++ b/query/lex.go
@@ -0,0 +1,211 @@
+package query
+
+import (
+	"fmt"
+	"strings"
+	"unicode"
+	"unicode/utf8"
+)
+
+// itemType identifies the type of lex items.
+type itemType int
+
+const eof = -1
+
+const (
+	itemError itemType = iota // error occurred;
+	// value is text of error
+	itemEOF
+	itemLeftParen  // (
+	itemRightParen // )
+	itemOr         // |
+	itemAnd        // ,
+	itemNot        // !
+	itemLt         // <<
+	itemLtEq       // <=, <
+	itemGt         // >>
+	itemGtEq       // >=, >
+	itemEq         // =
+	itemPatMatch   // %
+	itemRegexp     // ~
+	itemString
+)
+
+// item represents a token returned from the scanner.
+type item struct {
+	typ itemType // Type, such as itemNumber.
+	val string   // Value, such as "23.2".
+}
+
+func (i item) String() string {
+	if i.typ == itemString {
+		return fmt.Sprintf("%#v", i.val)
+	}
+	if i.typ == itemEOF {
+		return "<EOL>"
+	}
+	return i.val
+}
+
+// stateFn represents the state of the scanner
+// as a function that returns the next state.
+type stateFn func(*lexer) stateFn
+
+// lexer holds the state of the scanner.
+type lexer struct {
+	name  string    // used only for error reports.
+	input string    // the string being scanned.
+	start int       // start position of this item.
+	pos   int       // current position in the input.
+	width int       // width of last rune read from input.
+	items chan item // channel of scanned items.
+	last  item
+}
+
+func lex(name, input string) (*lexer, chan item) {
+	l := &lexer{
+		name:  name,
+		input: input,
+		items: make(chan item),
+	}
+	go l.run() // Concurrently run state machine.
+	return l, l.items
+}
+
+// emit passes an item back to the client.
+func (l *lexer) emit(t itemType) {
+	l.items <- item{t, l.input[l.start:l.pos]}
+	l.start = l.pos
+}
+
+// run lexes the input by executing state functions until
+// the state is nil.
+func (l *lexer) run() {
+	for state := lexMain; state != nil; {
+		state = state(l)
+	}
+	close(l.items) // No more tokens will be delivered.
+}
+
+// next returns the next rune in the input.
+func (l *lexer) next() (r rune) {
+	if l.pos >= len(l.input) {
+		l.width = 0
+		return eof
+	}
+	r, l.width =
+		utf8.DecodeRuneInString(l.input[l.pos:])
+	l.pos += l.width
+	return r
+}
+
+// ignore skips over the pending input before this point.
+func (l *lexer) ignore() {
+	l.start = l.pos
+}
+
+// backup steps back one rune.
+// Can be called only once per call of next.
+func (l *lexer) backup() {
+	l.pos -= l.width
+}
+
+// peek returns but does not consume
+// the next rune in the input.
+func (l *lexer) peek() rune {
+	r := l.next()
+	l.backup()
+	return r
+}
+
+func (l *lexer) Current() item {
+	if l.last.typ == 0 {
+		l.last = <-l.items
+	}
+
+	return l.last
+}
+
+func (l *lexer) Consume() {
+	l.last = <-l.items
+}
+
+// error returns an error token and terminates the scan
+// by passing back a nil pointer that will be the next
+// state, terminating l.run.
+func (l *lexer) errorf(format string, args ...interface{}) stateFn {
+	l.items <- item{
+		itemError,
+		fmt.Sprintf(format, args...),
+	}
+	return nil
+}
+
+func lexMain(l *lexer) stateFn {
+	switch r := l.next(); {
+	case r == eof:
+		l.emit(itemEOF)
+		return nil
+	case unicode.IsSpace(r):
+		l.ignore()
+	case r == '(':
+		l.emit(itemLeftParen)
+	case r == ')':
+		l.emit(itemRightParen)
+	case r == '|':
+		l.emit(itemOr)
+	case r == ',':
+		l.emit(itemAnd)
+	case r == '!':
+		l.emit(itemNot)
+	case r == '<':
+		r2 := l.next()
+		if r2 == '<' {
+			l.emit(itemLt)
+		} else if r2 == '=' {
+			l.emit(itemLtEq)
+		} else {
+			l.backup()
+			l.emit(itemLtEq)
+		}
+	case r == '>':
+		r2 := l.next()
+		if r2 == '>' {
+			l.emit(itemGt)
+		} else if r2 == '=' {
+			l.emit(itemGtEq)
+		} else {
+			l.backup()
+			l.emit(itemGtEq)
+		}
+	case r == '=':
+		l.emit(itemEq)
+	case r == '%':
+		l.emit(itemPatMatch)
+	case r == '~':
+		l.emit(itemRegexp)
+	default:
+		l.backup()
+		return lexString
+	}
+
+	return lexMain
+}
+
+func lexString(l *lexer) stateFn {
+	for {
+		r := l.next()
+		if unicode.IsSpace(r) || strings.IndexRune("()|,!<>=%~", r) > 0 {
+			l.backup()
+			l.emit(itemString)
+			return lexMain(l)
+		}
+
+		if r == eof {
+			l.emit(itemString)
+			l.emit(itemEOF)
+			return nil
+		}
+	}
+
+}
diff --git a/query/lex_test.go b/query/lex_test.go
new file mode 100644
index 00000000..6a492553
--- /dev/null
+++ b/query/lex_test.go
@@ -0,0 +1,46 @@
+package query
+
+import (
+	"fmt"
+	. "launchpad.net/gocheck"
+)
+
+type LexerSuite struct {
+}
+
+var _ = Suite(&LexerSuite{})
+
+func (s *LexerSuite) TestLexing(c *C) {
+	_, ch := lex("query", "package (<< 1.3), $Source | !app")
+
+	c.Check(<-ch, Equals, item{typ: itemString, val: "package"})
+	c.Check(<-ch, Equals, item{typ: itemLeftParen, val: "("})
+	c.Check(<-ch, Equals, item{typ: itemLt, val: "<<"})
+	c.Check(<-ch, Equals, item{typ: itemString, val: "1.3"})
+	c.Check(<-ch, Equals, item{typ: itemRightParen, val: ")"})
+	c.Check(<-ch, Equals, item{typ: itemAnd, val: ","})
+	c.Check(<-ch, Equals, item{typ: itemString, val: "$Source"})
+	c.Check(<-ch, Equals, item{typ: itemOr, val: "|"})
+	c.Check(<-ch, Equals, item{typ: itemNot, val: "!"})
+	c.Check(<-ch, Equals, item{typ: itemString, val: "app"})
+	c.Check(<-ch, Equals, item{typ: itemEOF, val: ""})
+}
+
+func (s *LexerSuite) TestConsume(c *C) {
+	l, _ := lex("query", "package (<< 1.3)")
+
+	c.Check(l.Current(), Equals, item{typ: itemString, val: "package"})
+	c.Check(l.Current(), Equals, item{typ: itemString, val: "package"})
+	l.Consume()
+	c.Check(l.Current(), Equals, item{typ: itemLeftParen, val: "("})
+	l.Consume()
+	c.Check(l.Current(), Equals, item{typ: itemLt, val: "<<"})
+}
+
+func (s *LexerSuite) TestString(c *C) {
+	l, _ := lex("query", "package (<< 1.3)")
+
+	c.Check(fmt.Sprintf("%s", l.Current()), Equals, "\"package\"")
+	l.Consume()
+	c.Check(fmt.Sprintf("%s", l.Current()), Equals, "(")
+}
diff --git a/query/query.go b/query/query.go
new file mode 100644
index 00000000..03e9c4a9
--- /dev/null
+++ b/query/query.go
@@ -0,0 +1,17 @@
+// Package query implements query language for
+package query
+
+/*
+
+  Query language resembling Debian dependencies and reprepro
+  queries: http://mirrorer.alioth.debian.org/reprepro.1.html
+
+  Query := A | A '|' Query
+  A := B | B ',' A
+  B := C | '!' B
+  C := '(' Query ')' | D
+  D := <field> <condition>
+  field := <package-name> | <field> | $special_field
+  condition := '(' <operator> value ')' |
+  operator := | << | < | <= | > | >> | >= | = | % | ~
+*/
diff --git a/query/query_test.go b/query/query_test.go
new file mode 100644
index 00000000..84989efd
--- /dev/null
+++ b/query/query_test.go
@@ -0,0 +1,11 @@
+package query
+
+import (
+	. "launchpad.net/gocheck"
+	"testing"
+)
+
+// Launch gocheck tests
+func Test(t *testing.T) {
+	TestingT(t)
+}
diff --git a/query/syntax.go b/query/syntax.go
new file mode 100644
index 00000000..bff3017f
--- /dev/null
+++ b/query/syntax.go
@@ -0,0 +1,164 @@
+package query
+
+import (
+	"fmt"
+	"github.com/smira/aptly/deb"
+	"strings"
+	"unicode"
+	"unicode/utf8"
+)
+
+type parser struct {
+	name  string // used only for error reports.
+	input *lexer // the input lexer
+	err   error  // error stored while parsing
+}
+
+func parse(input *lexer) (PackageQuery, error) {
+	p := &parser{
+		name:  input.name,
+		input: input,
+	}
+	query := p.parse()
+	if p.err != nil {
+		return nil, p.err
+	}
+	return query, nil
+}
+
+// Entry into parser
+func (p *parser) parse() PackageQuery {
+	defer func() {
+		if r := recover(); r != nil {
+			p.err = fmt.Errorf("parsing failed: %s", r)
+		}
+	}()
+
+	q := p.Query()
+	if p.input.Current().typ != itemEOF {
+		panic(fmt.Sprintf("unexpected token %s: expecting end of query", p.input.Current()))
+	}
+	return q
+}
+
+// Query := A | A '|' Query
+func (p *parser) Query() PackageQuery {
+	q := p.A()
+	if p.input.Current().typ == itemOr {
+		p.input.Consume()
+		return &OrQuery{L: q, R: p.Query()}
+	}
+	return q
+}
+
+// A := B | B ',' A
+func (p *parser) A() PackageQuery {
+	q := p.B()
+	if p.input.Current().typ == itemAnd {
+		p.input.Consume()
+		return &AndQuery{L: q, R: p.A()}
+	}
+	return q
+}
+
+// B := C | '!' B
+func (p *parser) B() PackageQuery {
+	if p.input.Current().typ == itemNot {
+		p.input.Consume()
+		return &NotQuery{Q: p.B()}
+	}
+	return p.C()
+}
+
+// C := '(' Query ')' | D
+func (p *parser) C() PackageQuery {
+	if p.input.Current().typ == itemLeftParen {
+		p.input.Consume()
+		q := p.Query()
+		if p.input.Current().typ != itemRightParen {
+			panic(fmt.Sprintf("unexpected token %s: expecting ')'", p.input.Current()))
+		}
+		p.input.Consume()
+		return q
+	}
+	return p.D()
+}
+
+func operatorToRelation(operator itemType) int {
+	switch operator {
+	case 0:
+		return deb.VersionDontCare
+	case itemLt:
+		return deb.VersionLess
+	case itemLtEq:
+		return deb.VersionLessOrEqual
+	case itemGt:
+		return deb.VersionGreater
+	case itemGtEq:
+		return deb.VersionGreaterOrEqual
+	case itemEq:
+		return deb.VersionEqual
+	case itemPatMatch:
+		return deb.VersionPatternMatch
+	case itemRegexp:
+		return deb.VersionRegexp
+	}
+	panic("unable to map token to relation")
+}
+
+// D := <field> <condition>
+// field := <package-name> | <field> | $special_field
+func (p *parser) D() PackageQuery {
+	if p.input.Current().typ != itemString {
+		panic(fmt.Sprintf("unexpected token %s: expecting field or package name", p.input.Current()))
+	}
+
+	field := p.input.Current().val
+	p.input.Consume()
+
+	operator, value := p.Condition()
+
+	r, _ := utf8.DecodeRuneInString(field)
+	if strings.HasPrefix(field, "$") || unicode.IsUpper(r) {
+		// special field or regular field
+		return &FieldQuery{Field: field, Relation: operatorToRelation(operator), Value: value}
+	}
+
+	// regular dependency-like query
+	return &DependencyQuery{Dep: deb.Dependency{Pkg: field, Relation: operatorToRelation(operator), Version: value}}
+}
+
+// condition := '(' <operator> value ')' |
+// operator := | << | < | <= | > | >> | >= | = | % | ~
+func (p *parser) Condition() (operator itemType, value string) {
+	if p.input.Current().typ != itemLeftParen {
+		return
+	}
+	p.input.Consume()
+
+	if p.input.Current().typ == itemLt ||
+		p.input.Current().typ == itemGt ||
+		p.input.Current().typ == itemLtEq ||
+		p.input.Current().typ == itemGtEq ||
+		p.input.Current().typ == itemEq ||
+		p.input.Current().typ == itemPatMatch ||
+		p.input.Current().typ == itemRegexp {
+		operator = p.input.Current().typ
+		p.input.Consume()
+	} else {
+		operator = itemEq
+	}
+
+	if p.input.Current().typ != itemString {
+		panic(fmt.Sprintf("unexpected token %s: expecting value", p.input.Current()))
+	}
+	value = p.input.Current().val
+	p.input.Consume()
+
+	if p.input.Current().typ != itemRightParen {
+		panic(fmt.Sprintf("unexpected token %s: expecting ')'", p.input.Current()))
+	}
+	p.input.Consume()
+
+	return
+}
diff --git a/query/syntax_test.go b/query/syntax_test.go
new file mode 100644
index 00000000..1711526d
--- /dev/null
+++ b/query/syntax_test.go
@@ -0,0 +1,64 @@
+package query
+
+import (
+	"github.com/smira/aptly/deb"
+	. "launchpad.net/gocheck"
+)
+
+type SyntaxSuite struct {
+}
+
+var _ = Suite(&SyntaxSuite{})
+
+func (s *SyntaxSuite) TestParsing(c *C) {
+	l, _ := lex("query", "package (<< 1.3), $Source")
+	q, err := parse(l)
+
+	c.Assert(err, IsNil)
+	c.Check(q.(*AndQuery).L, DeepEquals, &DependencyQuery{Dep: deb.Dependency{Pkg: "package", Relation: deb.VersionLess, Version: "1.3"}})
+	c.Check(q.(*AndQuery).R, DeepEquals, &FieldQuery{Field: "$Source"})
+
+	l, _ = lex("query", "package (1.3), Name (lala) | !$Source")
+	q, err = parse(l)
+
+	c.Assert(err, IsNil)
+	c.Check(q.(*OrQuery).L.(*AndQuery).L, DeepEquals, &DependencyQuery{Dep: deb.Dependency{Pkg: "package", Relation: deb.VersionEqual, Version: "1.3"}})
+	c.Check(q.(*OrQuery).L.(*AndQuery).R, DeepEquals, &FieldQuery{Field: "Name", Relation: deb.VersionEqual, Value: "lala"})
+	c.Check(q.(*OrQuery).R.(*NotQuery).Q, DeepEquals, &FieldQuery{Field: "$Source"})
+
+	l, _ = lex("query", "package, ((!(Name | $Source (~ a.*))))")
+	q, err = parse(l)
+
+	c.Assert(err, IsNil)
+	c.Check(q.(*AndQuery).L, DeepEquals, &DependencyQuery{Dep: deb.Dependency{Pkg: "package", Relation: deb.VersionDontCare}})
+	c.Check(q.(*AndQuery).R.(*NotQuery).Q.(*OrQuery).L, DeepEquals, &FieldQuery{Field: "Name", Relation: deb.VersionDontCare})
+	c.Check(q.(*AndQuery).R.(*NotQuery).Q.(*OrQuery).R, DeepEquals, &FieldQuery{Field: "$Source", Relation: deb.VersionRegexp, Value: "a.*"})
+
+	l, _ = lex("query", "package (> 5.3.7)")
+	q, err = parse(l)
+
+	c.Assert(err, IsNil)
+	c.Check(q, DeepEquals, &DependencyQuery{Dep: deb.Dependency{Pkg: "package", Relation: deb.VersionGreaterOrEqual, Version: "5.3.7"}})
+}
+
+func (s *SyntaxSuite) TestParsingErrors(c *C) {
+	l, _ := lex("query", "package (> 5.3.7), ")
+	_, err := parse(l)
+	c.Check(err, ErrorMatches, "parsing failed: unexpected token <EOL>: expecting field or package name")
+
+	l, _ = lex("query", "package>5.3.7)")
+	_, err = parse(l)
+	c.Check(err, ErrorMatches, "parsing failed: unexpected token >: expecting end of query")
+
+	l, _ = lex("query", "package | !|")
+	_, err = parse(l)
+	c.Check(err, ErrorMatches, "parsing failed: unexpected token |: expecting field or package name")
+
+	l, _ = lex("query", "((package )")
+	_, err = parse(l)
+	c.Check(err, ErrorMatches, "parsing failed: unexpected token <EOL>: expecting '\\)'")
+
+	l, _ = lex("query", "!package )")
+	_, err = parse(l)
+	c.Check(err, ErrorMatches, "parsing failed: unexpected token \\): expecting end of query")
+}
diff --git a/query/tree.go b/query/tree.go
new file mode 100644
index 00000000..6a507ac6
--- /dev/null
+++ b/query/tree.go
@@ -0,0 +1,62 @@
+package query
+
+import (
+	"github.com/smira/aptly/deb"
+)
+
+// PackageQuery is interface of predicate on Package
+type PackageQuery interface {
+	Matches(pkg *deb.Package) bool
+}
+
+// OrQuery is L | R
+type OrQuery struct {
+	L, R PackageQuery
+}
+
+// AndQuery is L , R
+type AndQuery struct {
+	L, R PackageQuery
+}
+
+// NotQuery is ! Q
+type NotQuery struct {
+	Q PackageQuery
+}
+
+// FieldQuery is generic request against field
+type FieldQuery struct {
+	Field    string
+	Relation int
+	Value    string
+}
+
+// DependencyQuery is generic Debian-dependency like query
+type DependencyQuery struct {
+	Dep deb.Dependency
+}
+
+// Matches if any of L, R matches
+func (q *OrQuery) Matches(pkg *deb.Package) bool {
+	return q.L.Matches(pkg) || q.R.Matches(pkg)
+}
+
+// Matches if both of L, R matches
+func (q *AndQuery) Matches(pkg *deb.Package) bool {
+	return q.L.Matches(pkg) && q.R.Matches(pkg)
+}
+
+// Matches if not matches
+func (q *NotQuery) Matches(pkg *deb.Package) bool {
+	return !q.Q.Matches(pkg)
+}
+
+// Matches on generic field
+func (q *FieldQuery) Matches(pkg *deb.Package) bool {
+	panic("not implemented yet")
+}
+
+// Matches on dependency condition
+func (q *DependencyQuery) Matches(pkg *deb.Package) bool {
+	return pkg.MatchesDependency(q.Dep)
+}