diff --git a/js/deno.ts b/js/deno.ts
index 1cc0a33d11..42bd380130 100644
--- a/js/deno.ts
+++ b/js/deno.ts
@@ -1,7 +1,7 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
 
 // Public deno module.
-export { pid, env, exit } from "./os";
+export { pid, env, exit, isTTY } from "./os";
 export { chdir, cwd } from "./dir";
 export {
   File,
diff --git a/js/os.ts b/js/os.ts
index 61b6ed9741..3122830cfa 100644
--- a/js/os.ts
+++ b/js/os.ts
@@ -21,6 +21,23 @@ interface CodeInfo {
   sourceCode: string | undefined;
 }
 
+/** Check if running in terminal.
+ *
+ *       import { isTTY } from "deno";
+ *       console.log(isTTY().stdout);
+ */
+export function isTTY(): { stdin: boolean; stdout: boolean; stderr: boolean } {
+  const builder = flatbuffers.createBuilder();
+  msg.IsTTY.startIsTTY(builder);
+  const inner = msg.IsTTY.endIsTTY(builder);
+  const baseRes = sendSync(builder, msg.Any.IsTTY, inner)!;
+  assert(msg.Any.IsTTYRes === baseRes.innerType());
+  const res = new msg.IsTTYRes();
+  assert(baseRes.inner(res) != null);
+
+  return { stdin: res.stdin(), stdout: res.stdout(), stderr: res.stderr() };
+}
+
 /** Exit the Deno process with optional exit code. */
 export function exit(exitCode = 0): never {
   const builder = flatbuffers.createBuilder();
diff --git a/js/os_test.ts b/js/os_test.ts
index 21ec5e69d0..0784fd5e40 100644
--- a/js/os_test.ts
+++ b/js/os_test.ts
@@ -27,3 +27,8 @@ test(function osPid() {
   console.log("pid", deno.pid);
   assert(deno.pid > 0);
 });
+
+// See complete tests in tools/is_tty_test.py
+test(function osIsTTYSmoke() {
+  console.log(deno.isTTY());
+});
diff --git a/src/msg.fbs b/src/msg.fbs
index 0bbc18b1d8..d7e71ab14f 100644
--- a/src/msg.fbs
+++ b/src/msg.fbs
@@ -61,7 +61,9 @@ union Any {
   RunStatus,
   RunStatusRes,
   Now,
-  NowRes
+  NowRes,
+  IsTTY,
+  IsTTYRes
 }
 
 enum ErrorKind: byte {
@@ -483,4 +485,12 @@ table NowRes {
   time: uint64;
 }
 
+table IsTTY {}
+
+table IsTTYRes {
+  stdin: bool;
+  stdout: bool;
+  stderr: bool;
+}
+
 root_type Base;
diff --git a/src/ops.rs b/src/ops.rs
index b17db87b21..b30473eb6d 100644
--- a/src/ops.rs
+++ b/src/ops.rs
@@ -1,4 +1,5 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+
 use crate::errors;
 use crate::errors::{DenoError, DenoResult, ErrorKind};
 use crate::fs as deno_fs;
@@ -18,6 +19,7 @@ use crate::resources::Resource;
 use crate::tokio_util;
 use crate::version;
 
+use atty;
 use flatbuffers::FlatBufferBuilder;
 use futures;
 use futures::Async;
@@ -121,6 +123,7 @@ pub fn dispatch(
       msg::Any::Write => op_write,
       msg::Any::WriteFile => op_write_file,
       msg::Any::Now => op_now,
+      msg::Any::IsTTY => op_is_tty,
       _ => panic!(format!(
         "Unhandled message {}",
         msg::enum_name_any(inner_type)
@@ -197,6 +200,31 @@ fn op_now(
   ))
 }
 
+fn op_is_tty(
+  _state: &Arc<IsolateState>,
+  base: &msg::Base<'_>,
+  _data: libdeno::deno_buf,
+) -> Box<Op> {
+  let builder = &mut FlatBufferBuilder::new();
+  let inner = msg::IsTTYRes::create(
+    builder,
+    &msg::IsTTYResArgs {
+      stdin: atty::is(atty::Stream::Stdin),
+      stdout: atty::is(atty::Stream::Stdout),
+      stderr: atty::is(atty::Stream::Stderr),
+    },
+  );
+  ok_future(serialize_response(
+    base.cmd_id(),
+    builder,
+    msg::BaseArgs {
+      inner: Some(inner.as_union_value()),
+      inner_type: msg::Any::IsTTYRes,
+      ..Default::default()
+    },
+  ))
+}
+
 fn op_exit(
   _config: &Arc<IsolateState>,
   base: &msg::Base<'_>,
diff --git a/tests/is_tty.ts b/tests/is_tty.ts
new file mode 100644
index 0000000000..a571aee186
--- /dev/null
+++ b/tests/is_tty.ts
@@ -0,0 +1,2 @@
+import { isTTY } from "deno";
+console.log(isTTY().stdin);
diff --git a/tools/is_tty_test.py b/tools/is_tty_test.py
new file mode 100755
index 0000000000..218e7f6208
--- /dev/null
+++ b/tools/is_tty_test.py
@@ -0,0 +1,24 @@
+#!/usr/bin/env python
+# Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+import os
+import pty
+import select
+import subprocess
+from util import build_path, executable_suffix
+from sys import stdin
+from permission_prompt_test import tty_capture
+
+IS_TTY_TEST_TS = "tests/is_tty.ts"
+
+def is_tty_test(deno_exe):
+    cmd = [deno_exe, IS_TTY_TEST_TS]
+    code, stdout, _ = tty_capture(cmd, b'')
+    assert code == 0
+    assert str(stdin.isatty()).lower() in stdout
+
+def main():
+    deno_exe = os.path.join(build_path(), "deno" + executable_suffix)
+    is_tty_test(deno_exe)
+
+if __name__ == "__main__":
+    main()
diff --git a/tools/test.py b/tools/test.py
index 8da13b01a9..246b094b73 100755
--- a/tools/test.py
+++ b/tools/test.py
@@ -66,12 +66,14 @@ def main(argv):
 
     integration_tests(deno_exe)
 
-    # TODO We currently skip testing the prompt in Windows completely.
+    # TODO We currently skip testing the prompt and IsTTY in Windows completely.
     # Windows does not support the pty module used for testing the permission
     # prompt.
     if os.name != 'nt':
         from permission_prompt_test import permission_prompt_test
+        from is_tty_test import is_tty_test
         permission_prompt_test(deno_exe)
+        is_tty_test(deno_exe)
 
     repl_tests(deno_exe)