diff --git a/doc/site/branching.markdown b/doc/site/branching.markdown
index e295be27..0561d1f8 100644
--- a/doc/site/branching.markdown
+++ b/doc/site/branching.markdown
@@ -57,3 +57,5 @@ An `||` ("logical or") expression is reversed. If the left-hand argument is trut
     :::wren
     io.write(false || 1)  // 1
     io.write(1 || 2)      // 1
+
+**TODO: Conditional operator.**
diff --git a/src/wren_compiler.c b/src/wren_compiler.c
index e4131460..2256644e 100644
--- a/src/wren_compiler.c
+++ b/src/wren_compiler.c
@@ -58,6 +58,7 @@ typedef enum
   TOKEN_AMPAMP,
   TOKEN_BANG,
   TOKEN_TILDE,
+  TOKEN_QUESTION,
   TOKEN_EQ,
   TOKEN_LT,
   TOKEN_GT,
@@ -431,6 +432,9 @@ static void makeToken(Parser* parser, TokenType type)
   parser->current.start = parser->tokenStart;
   parser->current.length = (int)(parser->currentChar - parser->tokenStart);
   parser->current.line = parser->currentLine;
+
+  // Make line tokens appear on the line containing the "\n".
+  if (type == TOKEN_LINE) parser->current.line--;
 }
 
 // If the current character is [c], then consumes it and makes a token of type
@@ -722,6 +726,7 @@ static void readRawToken(Parser* parser)
       case '%': makeToken(parser, TOKEN_PERCENT); return;
       case '+': makeToken(parser, TOKEN_PLUS); return;
       case '~': makeToken(parser, TOKEN_TILDE); return;
+      case '?': makeToken(parser, TOKEN_QUESTION); return;
       case '/':
         if (peekChar(parser) == '/')
         {
@@ -857,6 +862,7 @@ static void nextToken(Parser* parser)
       case TOKEN_AMPAMP:
       case TOKEN_BANG:
       case TOKEN_TILDE:
+      case TOKEN_QUESTION:
       case TOKEN_EQ:
       case TOKEN_LT:
       case TOKEN_GT:
@@ -1893,6 +1899,29 @@ void or(Compiler* compiler, bool allowAssignment)
   patchJump(compiler, jump);
 }
 
+void conditional(Compiler* compiler, bool allowAssignment)
+{
+  // Jump to the else branch if the condition is false.
+  int ifJump = emitJump(compiler, CODE_JUMP_IF);
+
+  // Compile the then branch.
+  parsePrecedence(compiler, allowAssignment, PREC_LOGIC);
+
+  consume(compiler, TOKEN_COLON,
+          "Expect ':' after then branch of conditional operator.");
+
+  // Jump over the else branch when the if branch is taken.
+  int elseJump = emitJump(compiler, CODE_JUMP);
+
+  // Compile the else branch.
+  patchJump(compiler, ifJump);
+
+  parsePrecedence(compiler, allowAssignment, PREC_ASSIGNMENT);
+
+  // Patch the jump over the else.
+  patchJump(compiler, elseJump);
+}
+
 void infixOp(Compiler* compiler, bool allowAssignment)
 {
   GrammarRule* rule = &rules[compiler->parser->previous.type];
@@ -1996,6 +2025,7 @@ GrammarRule rules[] =
   /* TOKEN_AMPAMP        */ INFIX(PREC_LOGIC, and),
   /* TOKEN_BANG          */ PREFIX_OPERATOR("!"),
   /* TOKEN_TILDE         */ PREFIX_OPERATOR("~"),
+  /* TOKEN_QUESTION      */ INFIX(PREC_ASSIGNMENT, conditional),
   /* TOKEN_EQ            */ UNUSED,
   /* TOKEN_LT            */ INFIX_OPERATOR(PREC_COMPARISON, "< "),
   /* TOKEN_GT            */ INFIX_OPERATOR(PREC_COMPARISON, "> "),
diff --git a/src/wren_core.c b/src/wren_core.c
index c4fcd5be..7a20200a 100644
--- a/src/wren_core.c
+++ b/src/wren_core.c
@@ -307,6 +307,10 @@ DEF_NATIVE(fn_call14) { return callFunction(vm, args, 14); }
 DEF_NATIVE(fn_call15) { return callFunction(vm, args, 15); }
 DEF_NATIVE(fn_call16) { return callFunction(vm, args, 16); }
 
+DEF_NATIVE(fn_toString)
+{
+  RETURN_VAL(wrenNewString(vm, "<fn>", 4));
+}
 
 DEF_NATIVE(list_add)
 {
@@ -921,6 +925,7 @@ void wrenInitializeCore(WrenVM* vm)
   NATIVE(vm->fnClass, "call              ", fn_call14);
   NATIVE(vm->fnClass, "call               ", fn_call15);
   NATIVE(vm->fnClass, "call                ", fn_call16);
+  NATIVE(vm->fnClass, "toString", fn_toString);
 
   vm->nullClass = defineClass(vm, "Null");
   NATIVE(vm->nullClass, "toString", null_toString);
diff --git a/test/conditional/conditional_in_then.wren b/test/conditional/conditional_in_then.wren
new file mode 100644
index 00000000..c98ab769
--- /dev/null
+++ b/test/conditional/conditional_in_then.wren
@@ -0,0 +1 @@
+1 ? 2 ? 3 : 4 : 5 // expect error
diff --git a/test/conditional/missing_colon.wren b/test/conditional/missing_colon.wren
new file mode 100644
index 00000000..2b69346a
--- /dev/null
+++ b/test/conditional/missing_colon.wren
@@ -0,0 +1,2 @@
+true ? 1 // expect error
+"next expression"
\ No newline at end of file
diff --git a/test/conditional/missing_condition.wren b/test/conditional/missing_condition.wren
new file mode 100644
index 00000000..7aee0864
--- /dev/null
+++ b/test/conditional/missing_condition.wren
@@ -0,0 +1 @@
+? 1 : 2 // expect error
diff --git a/test/conditional/missing_else.wren b/test/conditional/missing_else.wren
new file mode 100644
index 00000000..c5ce2ed2
--- /dev/null
+++ b/test/conditional/missing_else.wren
@@ -0,0 +1 @@
+true ? 1 : // expect error
diff --git a/test/conditional/missing_question.wren b/test/conditional/missing_question.wren
new file mode 100644
index 00000000..4804ecbd
--- /dev/null
+++ b/test/conditional/missing_question.wren
@@ -0,0 +1 @@
+true 1 : 2 // expect error
diff --git a/test/conditional/missing_then.wren b/test/conditional/missing_then.wren
new file mode 100644
index 00000000..9b1720ba
--- /dev/null
+++ b/test/conditional/missing_then.wren
@@ -0,0 +1 @@
+true ? : 2 // expect error
diff --git a/test/conditional/precedence.wren b/test/conditional/precedence.wren
new file mode 100644
index 00000000..a167a160
--- /dev/null
+++ b/test/conditional/precedence.wren
@@ -0,0 +1,59 @@
+class Foo {
+  static bar { return true }
+  static baz { return 1 }
+}
+
+// Condition precedence.
+IO.print(true ? 1 : 2) // expect: 1
+IO.print((true) ? 1 : 2) // expect: 1
+IO.print([true][0] ? 1 : 2) // expect: 1
+IO.print(Foo.bar ? 1 : 2) // expect: 1
+IO.print(3..4 ? 1 : 2) // expect: 1
+IO.print(3 * 4 ? 1 : 2) // expect: 1
+IO.print(3 + 4 ? 1 : 2) // expect: 1
+IO.print(true || false ? 1 : 2) // expect: 1
+IO.print(!false ? 1 : 2) // expect: 1
+IO.print(~0 ? 1 : 2) // expect: 1
+IO.print(3 is Num ? 1 : 2) // expect: 1
+IO.print(new Foo ? 1 : 2) // expect: 1
+IO.print(fn true ? 1 : 2) // expect: <fn>
+
+var a = 0
+IO.print(a = 3 ? 1 : 2) // expect: 1
+IO.print(a) // expect: 1
+
+// Then branch precedence.
+IO.print(true ? (1) : 2) // expect: 1
+IO.print(true ? [1][0] : 2) // expect: 1
+IO.print(true ? Foo.baz : 2) // expect: 1
+IO.print(true ? 3..4 : 2) // expect: 3..4
+IO.print(true ? 3 * 4 : 2) // expect: 12
+IO.print(true ? 3 + 4 : 2) // expect: 7
+IO.print(true ? 1 || false : 2) // expect: 1
+IO.print(true ? !true : 2) // expect: false
+IO.print(true ? ~0 : 2) // expect: 4294967295
+IO.print(true ? 3 is Bool : 2) // expect: false
+IO.print(true ? new Foo : 2) // expect: instance of Foo
+// TODO: Is this what we want?
+IO.print(true ? fn 1 : 2) // expect: <fn>
+
+IO.print(true ? a = 5 : 2) // expect: 5
+IO.print(a) // expect: 5
+
+// Else branch precedence.
+IO.print(false ? 1 : (2)) // expect: 2
+IO.print(false ? 1 : [2][0]) // expect: 2
+IO.print(false ? 2 : Foo.baz) // expect: 1
+IO.print(false ? 1 : 3..4) // expect: 3..4
+IO.print(false ? 1 : 3 * 4) // expect: 12
+IO.print(false ? 1 : 3 + 4) // expect: 7
+IO.print(false ? 1 : 2 || false) // expect: 2
+IO.print(false ? 1 : !false) // expect: true
+IO.print(false ? 1 : ~0) // expect: 4294967295
+IO.print(false ? 1 : 3 is Num) // expect: true
+IO.print(false ? 1 : new Foo) // expect: instance of Foo
+IO.print(false ? 1 : fn 2) // expect: <fn>
+
+// Associativity.
+IO.print(true ? 2 : true ? 4 : 5) // expect: 2
+IO.print(false ? 2 : true ? 4 : 5) // expect: 4
diff --git a/test/conditional/short_circuit.wren b/test/conditional/short_circuit.wren
new file mode 100644
index 00000000..21f37521
--- /dev/null
+++ b/test/conditional/short_circuit.wren
@@ -0,0 +1,2 @@
+true ? IO.print("ok") : IO.print("no") // expect: ok
+false ? IO.print("no") : IO.print("ok") // expect: ok
diff --git a/test/function/to_string.wren b/test/function/to_string.wren
new file mode 100644
index 00000000..c2c5821e
--- /dev/null
+++ b/test/function/to_string.wren
@@ -0,0 +1 @@
+IO.print(fn {}) // expect: <fn>