diff --git a/src/api/CMakeLists.txt b/src/api/CMakeLists.txt
index eb1b10759..40b2a1105 100644
--- a/src/api/CMakeLists.txt
+++ b/src/api/CMakeLists.txt
@@ -1,5 +1,5 @@
 add_library(api OBJECT string.cpp exception.cpp name.cpp options.cpp univ.cpp
-  expr.cpp decl.cpp env.cpp)
+  expr.cpp decl.cpp env.cpp ios.cpp)
 
 FILE(GLOB LEAN_API_INCLUDE_FILES lean*.h)
 install(FILES ${LEAN_API_INCLUDE_FILES} DESTINATION include)
diff --git a/src/api/ios.cpp b/src/api/ios.cpp
new file mode 100644
index 000000000..ef47ee52f
--- /dev/null
+++ b/src/api/ios.cpp
@@ -0,0 +1,88 @@
+/*
+Copyright (c) 2015 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+
+Author: Leonardo de Moura
+*/
+#include "frontends/lean/pp.h"
+#include "api/string.h"
+#include "api/exception.h"
+#include "api/ios.h"
+using namespace lean; // NOLINT
+
+lean_bool lean_ios_mk_std(lean_options o, lean_ios * r, lean_exception * ex) {
+    LEAN_TRY;
+    check_nonnull(o);
+    io_state ios(mk_pretty_formatter_factory(), to_options_ref(o));
+    *r = of_io_state(new io_state(ios));
+    LEAN_CATCH;
+}
+
+lean_bool lean_ios_mk_buffered(lean_options o, lean_ios * r, lean_exception * ex) {
+    LEAN_TRY;
+    check_nonnull(o);
+    io_state ios(mk_pretty_formatter_factory(), to_options_ref(o));
+    ios.set_regular_channel(std::make_shared<string_output_channel>());
+    ios.set_diagnostic_channel(std::make_shared<string_output_channel>());
+    *r = of_io_state(new io_state(ios));
+    LEAN_CATCH;
+}
+
+void lean_ios_del(lean_ios ios) {
+    delete to_io_state(ios);
+}
+
+lean_bool lean_ios_is_std(lean_ios ios) {
+    if (!ios)
+        return lean_false;
+    return dynamic_cast<string_output_channel*>(&to_io_state_ref(ios).get_regular_channel()) != nullptr;
+}
+
+lean_bool lean_ios_set_options(lean_ios ios, lean_options o, lean_exception * ex) {
+    LEAN_TRY;
+    check_nonnull(ios);
+    check_nonnull(o);
+    to_io_state(ios)->set_options(to_options_ref(o));
+    LEAN_CATCH;
+}
+
+lean_bool lean_ios_get_options(lean_ios ios, lean_options * r, lean_exception * ex) {
+    LEAN_TRY;
+    check_nonnull(ios);
+    *r = of_options(new options(to_io_state_ref(ios).get_options()));
+    LEAN_CATCH;
+}
+
+static void check_nonstd(lean_ios ios) {
+    check_nonnull(ios);
+    if (lean_ios_is_std(ios))
+        throw exception("invalid argument, buffered IO state expected");
+}
+
+lean_bool lean_ios_get_regular(lean_ios ios, char const ** r, lean_exception * ex) {
+    LEAN_TRY;
+    check_nonstd(ios);
+    *r = mk_string(static_cast<string_output_channel&>(to_io_state_ref(ios).get_regular_channel()).str());
+    LEAN_CATCH;
+}
+
+lean_bool lean_ios_get_diagnostic(lean_ios ios, char const ** r, lean_exception * ex) {
+    LEAN_TRY;
+    check_nonstd(ios);
+    *r = mk_string(static_cast<string_output_channel&>(to_io_state_ref(ios).get_diagnostic_channel()).str());
+    LEAN_CATCH;
+}
+
+lean_bool lean_ios_reset_regular(lean_ios ios, lean_exception * ex) {
+    LEAN_TRY;
+    check_nonstd(ios);
+    to_io_state(ios)->set_regular_channel(std::make_shared<string_output_channel>());
+    LEAN_CATCH;
+}
+
+lean_bool lean_ios_reset_diagnostic(lean_ios ios, lean_exception * ex) {
+    LEAN_TRY;
+    check_nonstd(ios);
+    to_io_state(ios)->set_diagnostic_channel(std::make_shared<string_output_channel>());
+    LEAN_CATCH;
+}
diff --git a/src/api/ios.h b/src/api/ios.h
new file mode 100644
index 000000000..9519e874a
--- /dev/null
+++ b/src/api/ios.h
@@ -0,0 +1,15 @@
+/*
+Copyright (c) 2015 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+
+Author: Leonardo de Moura
+*/
+#pragma once
+#include "library/io_state.h"
+#include "api/expr.h"
+#include "api/lean_ios.h"
+namespace lean {
+inline io_state * to_io_state(lean_ios n) { return reinterpret_cast<io_state *>(n); }
+inline io_state const & to_io_state_ref(lean_ios n) { return *reinterpret_cast<io_state *>(n); }
+inline lean_ios of_io_state(io_state * n) { return reinterpret_cast<lean_ios>(n); }
+}
diff --git a/src/api/lean_ios.h b/src/api/lean_ios.h
new file mode 100644
index 000000000..79715ec23
--- /dev/null
+++ b/src/api/lean_ios.h
@@ -0,0 +1,66 @@
+/*
+Copyright (c) 2015 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+
+Author: Leonardo de Moura
+*/
+#ifndef _LEAN_IOS_H
+#define _LEAN_IOS_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+   \defgroup capi C API
+*/
+/*@{*/
+
+/**
+   @name IO state API
+*/
+/*@{*/
+
+LEAN_DEFINE_TYPE(lean_ios);
+
+/** \brief Create IO state object that sends the regular and diagnostic output to standard out and standard error */
+lean_bool lean_ios_mk_std(lean_options o, lean_ios * r, lean_exception * ex);
+
+/** \brief Create IO state object that sends the regular and diagnostic output to string buffers. */
+lean_bool lean_ios_mk_buffered(lean_options o, lean_ios * r, lean_exception * ex);
+
+/** \brief Delete IO state object. */
+void lean_ios_del(lean_ios ios);
+
+/** \brief Return true iff it is standard IO state (i.e., it was created using #lean_ios_mk_std */
+lean_bool lean_ios_is_std(lean_ios ios);
+
+/** \brief Update the set of configurations options in the given IO state object */
+lean_bool lean_ios_set_options(lean_ios ios, lean_options o, lean_exception * ex);
+
+/** \brief Store in \c r the set of configuration options associated with the given IO state object. */
+lean_bool lean_ios_get_options(lean_ios ios, lean_options * r, lean_exception * ex);
+
+/** \brief Store in \c r the content of the regular output stream.
+    \pre !lean_ios_is_std(ios) */
+lean_bool lean_ios_get_regular(lean_ios ios, char const ** r, lean_exception * ex);
+
+/** \brief Store in \c r the content of the diagnostic output stream.
+    \pre !lean_ios_is_std(ios) */
+lean_bool lean_ios_get_diagnostic(lean_ios ios, char const ** r, lean_exception * ex);
+
+/** \brief Reset the regular output stream.
+    \pre !lean_ios_is_std(ios) */
+lean_bool lean_ios_reset_regular(lean_ios ios, lean_exception * ex);
+
+/** \brief Reset the diagnostic output stream.
+    \pre !lean_ios_is_std(ios) */
+lean_bool lean_ios_reset_diagnostic(lean_ios ios, lean_exception * ex);
+
+/*@}*/
+/*@}*/
+
+#ifdef __cplusplus
+};
+#endif
+#endif