diff --git a/lib/syntax_tree.rb b/lib/syntax_tree.rb
index 24d8426f..6c595db5 100644
--- a/lib/syntax_tree.rb
+++ b/lib/syntax_tree.rb
@@ -21,6 +21,7 @@ module SyntaxTree
   # CLI. Requiring those features takes time, so we autoload as many constants
   # as possible in order to keep the CLI as fast as possible.
 
+  autoload :Database, "syntax_tree/database"
   autoload :DSL, "syntax_tree/dsl"
   autoload :FieldVisitor, "syntax_tree/field_visitor"
   autoload :Index, "syntax_tree/index"
diff --git a/lib/syntax_tree/database.rb b/lib/syntax_tree/database.rb
new file mode 100644
index 00000000..c9981f35
--- /dev/null
+++ b/lib/syntax_tree/database.rb
@@ -0,0 +1,331 @@
+# frozen_string_literal: true
+
+module SyntaxTree
+  # Provides the ability to index source files into a database, then query for
+  # the nodes.
+  module Database
+    class IndexingVisitor < SyntaxTree::FieldVisitor
+      attr_reader :database, :filepath, :node_id
+
+      def initialize(database, filepath)
+        @database = database
+        @filepath = filepath
+        @node_id = nil
+      end
+
+      private
+
+      def comments(node)
+      end
+
+      def field(name, value)
+        return unless value.is_a?(SyntaxTree::Node)
+
+        binds = [node_id, visit(value), name]
+        database.execute(<<~SQL, binds)
+          INSERT INTO edges (from_id, to_id, name)
+          VALUES (?, ?, ?)
+        SQL
+      end
+
+      def list(name, values)
+        values.each_with_index do |value, index|
+          binds = [node_id, visit(value), name, index]
+          database.execute(<<~SQL, binds)
+            INSERT INTO edges (from_id, to_id, name, list_index)
+            VALUES (?, ?, ?, ?)
+          SQL
+        end
+      end
+
+      def node(node, _name)
+        previous = node_id
+        binds = [
+          node.class.name.delete_prefix("SyntaxTree::"),
+          filepath,
+          node.location.start_line,
+          node.location.start_column
+        ]
+
+        database.execute(<<~SQL, binds)
+          INSERT INTO nodes (type, path, line, column)
+          VALUES (?, ?, ?, ?)
+        SQL
+
+        begin
+          @node_id = database.last_insert_row_id
+          yield
+          @node_id
+        ensure
+          @node_id = previous
+        end
+      end
+
+      def text(name, value)
+      end
+
+      def pairs(name, values)
+        values.each_with_index do |(key, value), index|
+          binds = [node_id, visit(key), "#{name}[0]", index]
+          database.execute(<<~SQL, binds)
+            INSERT INTO edges (from_id, to_id, name, list_index)
+            VALUES (?, ?, ?, ?)
+          SQL
+
+          binds = [node_id, visit(value), "#{name}[1]", index]
+          database.execute(<<~SQL, binds)
+            INSERT INTO edges (from_id, to_id, name, list_index)
+            VALUES (?, ?, ?, ?)
+          SQL
+        end
+      end
+    end
+
+    # Query for a specific type of node.
+    class TypeQuery
+      attr_reader :type
+
+      def initialize(type)
+        @type = type
+      end
+
+      def each(database, &block)
+        sql = "SELECT * FROM nodes WHERE type = ?"
+        database.execute(sql, type).each(&block)
+      end
+    end
+
+    # Query for the attributes of a node, optionally also filtering by type.
+    class AttrQuery
+      attr_reader :type, :attrs
+
+      def initialize(type, attrs)
+        @type = type
+        @attrs = attrs
+      end
+
+      def each(database, &block)
+        joins = []
+        binds = []
+
+        attrs.each do |name, query|
+          ids = query.each(database).map { |row| row[0] }
+          joins << <<~SQL
+            JOIN edges AS #{name}
+            ON #{name}.from_id = nodes.id
+            AND #{name}.name = ?
+            AND #{name}.to_id IN (#{(["?"] * ids.size).join(", ")})
+          SQL
+
+          binds.push(name).concat(ids)
+        end
+
+        sql = +"SELECT nodes.* FROM nodes, edges #{joins.join(" ")}"
+
+        if type
+          sql << " WHERE nodes.type = ?"
+          binds << type
+        end
+
+        sql << " GROUP BY nodes.id"
+        database.execute(sql, binds).each(&block)
+      end
+    end
+
+    # Query for the results of either query.
+    class OrQuery
+      attr_reader :left, :right
+
+      def initialize(left, right)
+        @left = left
+        @right = right
+      end
+
+      def each(database, &block)
+        left.each(database, &block)
+        right.each(database, &block)
+      end
+    end
+
+    # A lazy query result.
+    class QueryResult
+      attr_reader :database, :query
+
+      def initialize(database, query)
+        @database = database
+        @query = query
+      end
+
+      def each(&block)
+        return enum_for(__method__) unless block_given?
+        query.each(database, &block)
+      end
+    end
+
+    # A pattern matching expression that will be compiled into a query.
+    class Pattern
+      class CompilationError < StandardError
+      end
+
+      attr_reader :query
+
+      def initialize(query)
+        @query = query
+      end
+
+      def compile
+        program =
+          begin
+            SyntaxTree.parse("case nil\nin #{query}\nend")
+          rescue Parser::ParseError
+            raise CompilationError, query
+          end
+
+        compile_node(program.statements.body.first.consequent.pattern)
+      end
+
+      private
+
+      def compile_error(node)
+        raise CompilationError, PP.pp(node, +"").chomp
+      end
+
+      # Shortcut for combining two queries into one that returns the results of
+      # if either query matches.
+      def combine_or(left, right)
+        OrQuery.new(left, right)
+      end
+
+      # in foo | bar
+      def compile_binary(node)
+        compile_error(node) if node.operator != :|
+
+        combine_or(compile_node(node.left), compile_node(node.right))
+      end
+
+      # in Ident
+      def compile_const(node)
+        value = node.value
+
+        if SyntaxTree.const_defined?(value, false)
+          clazz = SyntaxTree.const_get(value)
+          TypeQuery.new(clazz.name.delete_prefix("SyntaxTree::"))
+        else
+          compile_error(node)
+        end
+      end
+
+      # in SyntaxTree::Ident
+      def compile_const_path_ref(node)
+        parent = node.parent
+        if !parent.is_a?(SyntaxTree::VarRef) ||
+             !parent.value.is_a?(SyntaxTree::Const)
+          compile_error(node)
+        end
+
+        if parent.value.value == "SyntaxTree"
+          compile_node(node.constant)
+        else
+          compile_error(node)
+        end
+      end
+
+      # in Ident[value: String]
+      def compile_hshptn(node)
+        compile_error(node) unless node.keyword_rest.nil?
+
+        attrs = {}
+        node.keywords.each do |keyword, value|
+          compile_error(node) unless keyword.is_a?(SyntaxTree::Label)
+          attrs[keyword.value.chomp(":")] = compile_node(value)
+        end
+
+        type = node.constant ? compile_node(node.constant).type : nil
+        AttrQuery.new(type, attrs)
+      end
+
+      # in Foo
+      def compile_var_ref(node)
+        value = node.value
+
+        if value.is_a?(SyntaxTree::Const)
+          compile_node(value)
+        else
+          compile_error(node)
+        end
+      end
+
+      def compile_node(node)
+        case node
+        when SyntaxTree::Binary
+          compile_binary(node)
+        when SyntaxTree::Const
+          compile_const(node)
+        when SyntaxTree::ConstPathRef
+          compile_const_path_ref(node)
+        when SyntaxTree::HshPtn
+          compile_hshptn(node)
+        when SyntaxTree::VarRef
+          compile_var_ref(node)
+        else
+          compile_error(node)
+        end
+      end
+    end
+
+    class Connection
+      attr_reader :raw_connection
+
+      def initialize(raw_connection)
+        @raw_connection = raw_connection
+      end
+
+      def execute(query, binds = [])
+        raw_connection.execute(query, binds)
+      end
+
+      def index_file(filepath)
+        program = SyntaxTree.parse(SyntaxTree.read(filepath))
+        program.accept(IndexingVisitor.new(self, filepath))
+      end
+
+      def last_insert_row_id
+        raw_connection.last_insert_row_id
+      end
+
+      def prepare
+        raw_connection.execute(<<~SQL)
+          CREATE TABLE nodes (
+            id integer primary key,
+            type varchar(20),
+            path varchar(200),
+            line integer,
+            column integer
+          );
+        SQL
+
+        raw_connection.execute(<<~SQL)
+          CREATE INDEX nodes_type ON nodes (type);
+        SQL
+
+        raw_connection.execute(<<~SQL)
+          CREATE TABLE edges (
+            id integer primary key,
+            from_id integer,
+            to_id integer,
+            name varchar(20),
+            list_index integer
+          );
+        SQL
+
+        raw_connection.execute(<<~SQL)
+          CREATE INDEX edges_name ON edges (name);
+        SQL
+      end
+
+      def search(query)
+        QueryResult.new(self, Pattern.new(query).compile)
+      end
+    end
+  end
+end