diff --git a/assets/parser.d.erb b/assets/parser.d.erb
index ff25d2c..41ad6ef 100644
--- a/assets/parser.d.erb
+++ b/assets/parser.d.erb
@@ -124,14 +124,19 @@ class <%= @classname %>
             uint code_id;
         }
 
-<% transition_table, state_table = @lexer.build_tables %>
+        private struct Mode
+        {
+            uint state_table_offset;
+        }
+
+<% transition_table, state_table, mode_table = @lexer.build_tables %>
         private static immutable Transition transitions[] = [
 <% transition_table.each do |transition_table_entry| %>
             Transition(<%= transition_table_entry[:first] %>u, <%= transition_table_entry[:last] %>u, <%= transition_table_entry[:destination] %>u),
 <% end %>
         ];
 
-        private static const State states[] = [
+        private static immutable State states[] = [
 <% state_table.each do |state_table_entry| %>
             State(<%= state_table_entry[:transition_table_index] %>u,
                   <%= state_table_entry[:n_transitions] %>u,
@@ -140,6 +145,12 @@ class <%= @classname %>
 <% end %>
         ];
 
+        private static immutable Mode modes[] = [
+<% mode_table.each do |mode_table_entry| %>
+            Mode(<%= mode_table_entry[:state_table_offset] %>),
+<% end %>
+        ];
+
         struct LexedToken
         {
             size_t row;
@@ -153,11 +164,13 @@ class <%= @classname %>
         private size_t m_input_position;
         private size_t m_input_row;
         private size_t m_input_col;
+        private size_t m_mode;
 
         this(const(ubyte) * input, size_t input_length)
         {
             m_input = input;
             m_input_length = input_length;
+            m_mode = <%= @lexer.mode_id("default") %>;
         }
 
         LexedToken lex_token()
@@ -211,7 +224,7 @@ class <%= @classname %>
             MatchInfo longest_match_info;
             longest_match_info.token = _TOKEN_COUNT;
             MatchInfo attempt_match_info;
-            uint current_state;
+            uint current_state = modes[m_mode].state_table_offset;
             for (;;)
             {
                 auto decoded = Decoder.decode_code_point(&m_input[m_input_position + attempt_match_info.length], m_input_length - m_input_position - attempt_match_info.length);
diff --git a/lib/propane/generator.rb b/lib/propane/generator.rb
index 8f37416..5645999 100644
--- a/lib/propane/generator.rb
+++ b/lib/propane/generator.rb
@@ -26,6 +26,17 @@ class Propane
     private
 
     def process_grammar!
+      # Assign default pattern mode to patterns without a mode assigned.
+      found_default = false
+      @grammar.patterns.each do |pattern|
+        if pattern.mode.nil?
+          pattern.mode = "default"
+          found_default = true
+        end
+      end
+      unless found_default
+        raise Error.new("No patterns found for default mode")
+      end
       # Add EOF token.
       @grammar.tokens << Token.new("$EOF", nil)
       tokens_by_name = {}
@@ -152,6 +163,13 @@ class Propane
     def expand_code(code)
       code.gsub(/\$token\(([$\w]+)\)/) do |match|
         "TOKEN_#{Token.code_name($1)}"
+      end.gsub(/\$mode\(([a-zA-Z_][a-zA-Z_0-9]*)\)/) do |match|
+        mode_name = $1
+        mode_id = @lexer.mode_id(mode_name)
+        unless mode_id
+          raise Error.new("Lexer mode '#{mode_name}' not found")
+        end
+        "m_mode = #{mode_id}u"
       end
     end
 
diff --git a/lib/propane/lexer.rb b/lib/propane/lexer.rb
index 59bbd17..96c2a6f 100644
--- a/lib/propane/lexer.rb
+++ b/lib/propane/lexer.rb
@@ -1,51 +1,74 @@
 class Propane
   class Lexer
 
-    # @return [DFA]
-    #   Lexer DFA.
-    attr_accessor :dfa
-
     def initialize(grammar)
       @grammar = grammar
-      @dfa = DFA.new(grammar.patterns)
     end
 
     def build_tables
+      @modes = @grammar.patterns.group_by do |pattern|
+        pattern.mode
+      end.transform_values do |patterns|
+        {dfa: DFA.new(patterns)}
+      end
+      @modes.each_with_index do |(mode_name, mode_info), index|
+        mode_info[:id] = index
+      end
       transition_table = []
       state_table = []
-      states = @dfa.enumerate
-      states.each do |state, id|
-        token =
-          if state.accepts.nil?
-            @grammar.tokens.size
-          elsif state.accepts.drop?
-            TOKEN_DROP
-          elsif state.accepts.token
-            state.accepts.token.id
-          else
-            @grammar.tokens.size
-          end
-        code_id =
-          if state.accepts && state.accepts.code_id
-            state.accepts.code_id
-          else
-            0xFFFF_FFFF
-          end
-        state_table << {
-          transition_table_index: transition_table.size,
-          n_transitions: state.transitions.size,
-          token: token,
-          code_id: code_id,
+      mode_table = []
+      @modes.each do |mode_name, mode_info|
+        state_table_offset = state_table.size
+        mode_table << {
+          state_table_offset: state_table_offset,
         }
-        state.transitions.each do |transition|
-          transition_table << {
-            first: transition.code_point_range.first,
-            last: transition.code_point_range.last,
-            destination: states[transition.destination],
+        states = mode_info[:dfa].enumerate
+        states.each do |state, id|
+          token =
+            if state.accepts.nil?
+              @grammar.tokens.size
+            elsif state.accepts.drop?
+              TOKEN_DROP
+            elsif state.accepts.token
+              state.accepts.token.id
+            else
+              @grammar.tokens.size
+            end
+          code_id =
+            if state.accepts && state.accepts.code_id
+              state.accepts.code_id
+            else
+              0xFFFF_FFFF
+            end
+          state_table << {
+            transition_table_index: transition_table.size,
+            n_transitions: state.transitions.size,
+            token: token,
+            code_id: code_id,
           }
+          state.transitions.each do |transition|
+            transition_table << {
+              first: transition.code_point_range.first,
+              last: transition.code_point_range.last,
+              destination: states[transition.destination] + state_table_offset,
+            }
+          end
         end
       end
-      [transition_table, state_table]
+      [transition_table, state_table, mode_table]
+    end
+
+    # Get ID for a mode.
+    #
+    # @param mode_name [String]
+    #   Mode name.
+    #
+    # @return [Integer, nil]
+    #   Mode ID.
+    def mode_id(mode_name)
+      if mode_info = @modes[mode_name]
+        mode_info[:id]
+      end
     end
 
   end
diff --git a/lib/propane/pattern.rb b/lib/propane/pattern.rb
index 80b8048..a111eac 100644
--- a/lib/propane/pattern.rb
+++ b/lib/propane/pattern.rb
@@ -28,7 +28,7 @@ class Propane
 
     # @return [String, nil]
     #   Lexer mode for this pattern.
-    attr_reader :mode
+    attr_accessor :mode
 
     # Construct a Pattern.
     #
diff --git a/spec/propane_spec.rb b/spec/propane_spec.rb
index 64e4779..2e75d96 100644
--- a/spec/propane_spec.rb
+++ b/spec/propane_spec.rb
@@ -192,4 +192,37 @@ EOF
       "def!",
     ])
   end
+
+  it "supports lexer modes" do
+    write_grammar <<EOF
+token abc;
+token def;
+tokenid string;
+drop /\\s+/;
+/"/ <<
+  writeln("begin string mode");
+  $mode(string);
+>>
+string: /[^"]+/ <<
+  writeln("captured string");
+>>
+string: /"/ <<
+  $mode(default);
+  return $token(string);
+>>
+Start -> abc string def;
+EOF
+    build_parser
+    compile("spec/test_lexer_modes.d")
+    results = run
+    expect(results.status).to eq 0
+    verify_lines(results.stdout, [
+      "begin string mode",
+      "captured string",
+      "pass1",
+      "begin string mode",
+      "captured string",
+      "pass2",
+    ])
+  end
 end
diff --git a/spec/test_lexer_modes.d b/spec/test_lexer_modes.d
new file mode 100644
index 0000000..c1f7b27
--- /dev/null
+++ b/spec/test_lexer_modes.d
@@ -0,0 +1,20 @@
+import testparser;
+import std.stdio;
+
+int main()
+{
+    return 0;
+}
+
+unittest
+{
+    string input = `abc "a string" def`;
+    auto parser = new Testparser.Parser(cast(const(ubyte) *)input.ptr, input.length);
+    assert(parser.parse() == true);
+    writeln("pass1");
+
+    input = `abc "abc def" def`;
+    parser = new Testparser.Parser(cast(const(ubyte) *)input.ptr, input.length);
+    assert(parser.parse() == true);
+    writeln("pass2");
+}