diff --git a/toolkit/components/glean/api/src/ffi/mod.rs b/toolkit/components/glean/api/src/ffi/mod.rs
index 9d3a70ff2403..ffbab3b0dbf3 100644
--- a/toolkit/components/glean/api/src/ffi/mod.rs
+++ b/toolkit/components/glean/api/src/ffi/mod.rs
@@ -22,6 +22,38 @@ define_metric_ffi!(TIMESPAN_MAP {
     stop -> fog_timespan_stop(),
 });
 
+// The String functions are custom because test_get needs to use an outparam.
+// If we can make test_get optional, we can go back to using the macro to
+// generate the rest of the functions, or something.
+
+#[no_mangle]
+pub extern "C" fn fog_string_test_has_value(id: u32, storage_name: FfiStr) -> u8 {
+    match crate::metrics::__glean_metric_maps::STRING_MAP.get(&id.into()) {
+        Some(metric) => metric.test_get_value(storage_name.as_str()).is_some() as u8,
+        None => panic!("No metric for id {}", id),
+    }
+}
+
+#[cfg(feature = "with_gecko")]
+#[no_mangle]
+pub extern "C" fn fog_string_test_get_value(id: u32, storage_name: FfiStr, value: &mut nsACString) {
+    match crate::metrics::__glean_metric_maps::STRING_MAP.get(&id.into()) {
+        Some(metric) => {
+            value.assign(&metric.test_get_value(storage_name.as_str()).unwrap());
+        }
+        None => panic!("No metric for id {}", id),
+    }
+}
+
+#[cfg(feature = "with_gecko")]
+#[no_mangle]
+pub extern "C" fn fog_string_set(id: u32, value: &nsACString) {
+    match crate::metrics::__glean_metric_maps::STRING_MAP.get(&id.into()) {
+        Some(metric) => metric.set(value.to_utf8()),
+        None => panic!("No metric for id {}", id),
+    }
+}
+
 // The Uuid functions are custom because test_get needs to use an outparam.
 // If we can make test_get optional, we can go back to using the macro to
 // generate the rest of the functions, or something.
diff --git a/toolkit/components/glean/bindings/MetricTypes.h b/toolkit/components/glean/bindings/MetricTypes.h
index 34cbd696d077..15dd1dd64ae6 100644
--- a/toolkit/components/glean/bindings/MetricTypes.h
+++ b/toolkit/components/glean/bindings/MetricTypes.h
@@ -7,6 +7,7 @@
 
 #include "mozilla/glean/Counter.h"
 #include "mozilla/glean/Timespan.h"
+#include "mozilla/glean/String.h"
 #include "mozilla/glean/Uuid.h"
 
 #endif  // mozilla_Glean_MetricTypes_h
diff --git a/toolkit/components/glean/bindings/private/String.cpp b/toolkit/components/glean/bindings/private/String.cpp
new file mode 100644
index 000000000000..98d7dffa3a0b
--- /dev/null
+++ b/toolkit/components/glean/bindings/private/String.cpp
@@ -0,0 +1,41 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/glean/String.h"
+
+#include "nsString.h"
+#include "mozilla/Components.h"
+#include "nsIClassInfoImpl.h"
+
+namespace mozilla {
+namespace glean {
+
+NS_IMPL_CLASSINFO(GleanString, nullptr, 0, {0})
+NS_IMPL_ISUPPORTS_CI(GleanString, nsIGleanString)
+
+NS_IMETHODIMP
+GleanString::Set(const nsACString& value, JSContext* cx) {
+  this->mString.Set(value);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+GleanString::TestHasValue(const nsACString& aStorageName, JSContext* cx,
+                          bool* result) {
+  *result = this->mString.TestHasValue(PromiseFlatCString(aStorageName).get());
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+GleanString::TestGetValue(const nsACString& aStorageName, JSContext* cx,
+                          nsACString& result) {
+  result.Assign(
+      this->mString.TestGetValue(PromiseFlatCString(aStorageName).get()));
+  return NS_OK;
+}
+
+}  // namespace glean
+}  // namespace mozilla
diff --git a/toolkit/components/glean/bindings/private/String.h b/toolkit/components/glean/bindings/private/String.h
new file mode 100644
index 000000000000..d4a2cb7c6be9
--- /dev/null
+++ b/toolkit/components/glean/bindings/private/String.h
@@ -0,0 +1,97 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_glean_GleanString_h
+#define mozilla_glean_GleanString_h
+
+#include "nsIGleanMetrics.h"
+#include "nsString.h"
+
+namespace mozilla {
+namespace glean {
+
+namespace impl {
+extern "C" {
+void fog_string_set(uint32_t id, const nsACString& value);
+uint32_t fog_string_test_has_value(uint32_t id, const char* storageName);
+void fog_string_test_get_value(uint32_t id, const char* storageName,
+                               nsACString& value);
+}
+
+class StringMetric {
+ public:
+  constexpr explicit StringMetric(uint32_t id) : mId(id) {}
+
+  /*
+   * Set to the specified value.
+   *
+   * Truncates the value if it is longer than 100 bytes and logs an error.
+   * See https://mozilla.github.io/glean/book/user/metrics/string.html#limits.
+   *
+   * @param value The string to set the metric to.
+   */
+  void Set(const nsACString& value) const { fog_string_set(mId, value); }
+
+  /**
+   * **Test-only API**
+   *
+   * Tests whether a value is stored for the metric.
+   *
+   * This function will attempt to await the last parent-process task (if any)
+   * writing to the the metric's storage engine before returning a value.
+   * This function will not wait for data from child processes.
+   *
+   * Parent process only. Panics in child processes.
+   *
+   * @param aStorageName the name of the ping to retrieve the metric for.
+   * @return true if metric value exists, otherwise false
+   */
+  bool TestHasValue(const char* aStorageName) const {
+    return fog_string_test_has_value(mId, aStorageName) != 0;
+  }
+
+  /**
+   * **Test-only API**
+   *
+   * Gets the currently stored value as a string.
+   *
+   * This function will attempt to await the last parent-process task (if any)
+   * writing to the the metric's storage engine before returning a value.
+   * This function will not wait for data from child processes.
+   *
+   * This doesn't clear the stored value.
+   * Parent process only. Panics in child processes.
+   *
+   * @return value of the stored metric.
+   */
+  nsCString TestGetValue(const char* aStorageName) const {
+    nsCString ret;
+    fog_string_test_get_value(mId, aStorageName, ret);
+    return ret;
+  }
+
+ private:
+  const uint32_t mId;
+};
+}  // namespace impl
+
+class GleanString final : public nsIGleanString {
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIGLEANSTRING
+
+  explicit GleanString(uint32_t id) : mString(id){};
+
+ private:
+  virtual ~GleanString() = default;
+
+  const impl::StringMetric mString;
+};
+
+}  // namespace glean
+}  // namespace mozilla
+
+#endif /* mozilla_glean_GleanString.h */
diff --git a/toolkit/components/glean/build_scripts/glean_parser_ext/util.py b/toolkit/components/glean/build_scripts/glean_parser_ext/util.py
index c11885255281..42b29909de82 100644
--- a/toolkit/components/glean/build_scripts/glean_parser_ext/util.py
+++ b/toolkit/components/glean/build_scripts/glean_parser_ext/util.py
@@ -29,7 +29,7 @@ def generate_metric_ids(objs):
     return lambda metric: metric_id_mapping[(metric.category, metric.name)]
 
 
-IMPLEMENTED_CPP_TYPES = ["counter", "timespan", "uuid"]
+IMPLEMENTED_CPP_TYPES = ["counter", "string", "timespan", "uuid"]
 
 
 def is_implemented_metric_type(typ):
diff --git a/toolkit/components/glean/gtest/TestFog.cpp b/toolkit/components/glean/gtest/TestFog.cpp
index d4b58a71b18b..f27495809752 100644
--- a/toolkit/components/glean/gtest/TestFog.cpp
+++ b/toolkit/components/glean/gtest/TestFog.cpp
@@ -59,6 +59,18 @@ TEST(FOG, TestCppCounterWorks)
   ASSERT_EQ(42, mozilla::glean::test_only::bad_code.TestGetValue("test-ping"));
 }
 
+TEST(FOG, TestCppStringWorks)
+{
+  auto kValue = "cheez!"_ns;
+  mozilla::glean::test_only::cheesy_string.Set(kValue);
+
+  ASSERT_TRUE(
+      mozilla::glean::test_only::cheesy_string.TestHasValue("test-ping"));
+  ASSERT_STREQ(
+      kValue.get(),
+      mozilla::glean::test_only::cheesy_string.TestGetValue("test-ping").get());
+}
+
 TEST(FOG, TestCppTimespanWorks)
 {
   mozilla::glean::test_only::can_we_time_it.Start();
diff --git a/toolkit/components/glean/moz.build b/toolkit/components/glean/moz.build
index af8ce301a063..2d4986c0cc16 100644
--- a/toolkit/components/glean/moz.build
+++ b/toolkit/components/glean/moz.build
@@ -23,6 +23,7 @@ if CONFIG["MOZ_GLEAN"]:
         "bindings/Glean.h",
         "bindings/MetricTypes.h",
         "bindings/private/Counter.h",
+        "bindings/private/String.h",
         "bindings/private/Timespan.h",
         "bindings/private/Uuid.h",
     ]
@@ -31,6 +32,7 @@ if CONFIG["MOZ_GLEAN"]:
         "bindings/Category.cpp",
         "bindings/Glean.cpp",
         "bindings/private/Counter.cpp",
+        "bindings/private/String.cpp",
         "bindings/private/Timespan.cpp",
         "bindings/private/Uuid.cpp",
         "ipc/FOGIPC.cpp",
diff --git a/toolkit/components/glean/test_metrics.yaml b/toolkit/components/glean/test_metrics.yaml
index 4dbff75c954e..119ec60f0472 100644
--- a/toolkit/components/glean/test_metrics.yaml
+++ b/toolkit/components/glean/test_metrics.yaml
@@ -47,6 +47,23 @@ test_only:
     send_in_pings:
       - test-ping
 
+  cheesy_string:
+    type: string
+    description: |
+      Only the cheesiest of strings.
+      This is a test-only metric.
+    bugs:
+      - https://bugzilla.mozilla.org/show_bug.cgi?id=1673662
+    data_reviews:
+      - https://bugzilla.mozilla.org/show_bug.cgi?id=1673662#c1
+    data_sensitivity:
+      - technical
+    notification_emails:
+      - glean-team@mozilla.com
+    expires: never
+    send_in_pings:
+      - test-ping
+
   what_id_it:  # Using a different metrics yaml style for fun.
     type: uuid
     description: |
diff --git a/toolkit/components/glean/xpcom/nsIGleanMetrics.idl b/toolkit/components/glean/xpcom/nsIGleanMetrics.idl
index 08c666d68524..2c1d1aa53e19 100644
--- a/toolkit/components/glean/xpcom/nsIGleanMetrics.idl
+++ b/toolkit/components/glean/xpcom/nsIGleanMetrics.idl
@@ -51,6 +51,52 @@ interface nsIGleanCounter : nsISupports
   long testGetValue(in ACString aStorageName);
 };
 
+[scriptable, uuid(d84a3555-46f1-48c1-9122-e8e88b069d2b)]
+interface nsIGleanString : nsISupports
+{
+  /*
+  * Set to the specified value.
+  *
+  * @param value The string to set the metric to.
+  */
+  [implicit_jscontext]
+  void set(in ACString value);
+
+  /**
+   * **Test-only API**
+   *
+   * Tests whether a value is stored for the metric.
+   *
+   * This function will attempt to await the last parent-process task (if any)
+   * writing to the the metric's storage engine before returning a value.
+   * This function will not wait for data from child processes.
+   *
+   * Parent process only. Panics in child processes.
+   *
+   * @param aStorageName the name of the ping to retrieve the metric for.
+   * @return true if metric value exists, otherwise false
+   */
+  [implicit_jscontext]
+  bool testHasValue(in ACString aStorageName);
+
+  /**
+   * **Test-only API**
+   *
+   * Gets the currently stored value as a string.
+   *
+   * This function will attempt to await the last parent-process task (if any)
+   * writing to the the metric's storage engine before returning a value.
+   * This function will not wait for data from child processes.
+   *
+   * This doesn't clear the stored value.
+   * Parent process only. Panics in child processes.
+   *
+   * @return value of the stored metric.
+   */
+  [implicit_jscontext]
+  ACString testGetValue(in ACString aStorageName);
+};
+
 [scriptable, uuid(2586530c-030f-11eb-93cb-cbf30d25225a)]
 interface nsIGleanTimespan : nsISupports
 {
diff --git a/toolkit/components/glean/xpcshell/test_Glean.js b/toolkit/components/glean/xpcshell/test_Glean.js
index b33b3f6c2de2..bc5532ef08e6 100644
--- a/toolkit/components/glean/xpcshell/test_Glean.js
+++ b/toolkit/components/glean/xpcshell/test_Glean.js
@@ -32,6 +32,14 @@ add_task(function test_fog_counter_works() {
   Assert.equal(31, Glean.test_only.bad_code.testGetValue("test-ping"));
 });
 
+add_task(async function test_fog_string_works() {
+  const value = "a cheesy string!";
+  Glean.test_only.cheesy_string.set(value);
+
+  Assert.ok(Glean.test_only.cheesy_string.testHasValue("test-ping"));
+  Assert.equal(value, Glean.test_only.cheesy_string.testGetValue("test-ping"));
+});
+
 add_task(async function test_fog_timespan_works() {
   // We start, briefly sleep and then stop.
   // That guarantees some time to measure.