diff --git a/README.md b/README.md
index 4beab08..85a588e 100644
--- a/README.md
+++ b/README.md
@@ -58,7 +58,7 @@ All of the above Launch5j variants are available as `i586` (32-Bit) and `x86-64`
 
 Launch5j comes with a *default* executable icon and a *default* splash screen bitmap. These just server as an example and you probably want to replace them with your own *application-specific* graphics.
 
-It is ***not*** necessary to re-build the executable files for that purpose. Instead, you can simply use a resource editor, such as [**XN Resource Editor**](https://stefansundin.github.io/xn_resource_editor/) or [**Resource Hacker™**](http://www.angusj.com/resourcehacker/), to *modify* the pre-compiled executable files as needed:  
+It is ***not*** necessary to re-build the executable files for that purpose. Instead, you can simply use a resource editor, such as [**XN Resource Editor**](https://web.archive.org/web/20100419201225/http://www.wilsonc.demon.co.uk/d10resourceeditor.htm) ([mirror](https://stefansundin.github.io/xn_resource_editor/)) or [**Resource Hacker™**](http://www.angusj.com/resourcehacker/), to *modify* the pre-compiled executable files as needed:  
 
 ![reshack](etc/reshacker-example.png)
 
@@ -90,17 +90,30 @@ Some options can be configured via the launcher executable's [STRINGTABLE](https
   Specifies the ***maximum*** supported JRE version, in the **`w.x.y.z`** format (e.g. `12.0.0.0`).  
   This values is *exclusive*, i.e. only JRE versions *older* than the specified JRE version will be accepted.  
   If not specified, then there is **no** upper limit on the supported JRE version.
-
-  *Hint:* Old-style `1.x.y.z` Java versions  are automatically translated to the `x.y.z.0` format!
-
+  
+  *Hint:* Old-style `1.x.y.z` Java versions are automatically translated to the `x.y.z.0` format!
+  
   (This option only applies to the `registry` variant of Launch5j)
 
 * **`ID_STR_BITNESS` (#6)**  
   Specifies the required ***bitness*** of the JRE. This can be either **`32`** (x86, aka i586) or **`64`** (x86-64).  
   If not specified, 32-Bit *and* 64-Bit JREs are accepted, with a preference to 64-Bit.
-
+  
   (This option only applies to the `registry` variant of Launch5j)
 
+* **`ID_STR_BITNESS` (#6)**  
+  Specifies the required ***bitness*** of the JRE. This can be either **`32`** (x86, aka i586) or **`64`** (x86-64).  
+  If not specified, 32-Bit *and* 64-Bit JREs are accepted, with a preference to 64-Bit.
+  
+  (This option only applies to the `registry` variant of Launch5j)
+
+* **`ID_STR_MUTEXID` (#7)**  
+  Specifies the application ID to be used when creating the [*single-instance*](http://www.bcbjournal.org/articles/vol3/9911/Single-instance_applications.htm) mutex.  
+  The ID **must** be at least 5 characters in length and **should** be a *unique* string for each application!  
+  If not specified, then **no** mutex will be created and thus *multiple* instances will be allowed.
+  
+  *Hint:* If the specified application ID *starts* with an **`@`** character, then Launch5j will **not** show a message box when the application is already running; the **`@`** character is *not* considered a part of the actual ID.
+
 *Note:* We use the convention that the default resource string value `"?"` is used to represent an “undefined” value, because resource strings cannot be empty. You can replace the default value as needed!
 
 # Build instructions
diff --git a/build.cmd b/build.cmd
index cf0030d..93bec23 100644
--- a/build.cmd
+++ b/build.cmd
@@ -27,7 +27,7 @@ for %%m in (32,64) do (
 	echo.
 )
 
-echo ALL IS COMPLETED.
+echo ALL IS DONE.
 
 :build_completed
 pause
diff --git a/res/common.rc b/res/common.rc
index ac79083..7f9b9cf 100644
--- a/res/common.rc
+++ b/res/common.rc
@@ -40,6 +40,7 @@ BEGIN
     ID_STR_HEADING L"?" /*custom application title*/
     ID_STR_JVMARGS L"?" /*additional JVM args*/
     ID_STR_CMDARGS L"?" /*additional command-line args*/
+    ID_STR_MUTEXID L"?" /*single instance mutex ID*/
 END
 
 /////////////////////////////////////////////////////////////////////////////
diff --git a/src/head.c b/src/head.c
index 38c37d5..112982c 100644
--- a/src/head.c
+++ b/src/head.c
@@ -48,6 +48,7 @@
 // Const
 static const wchar_t *const JRE_RELATIVE_PATH = L"runtime\\bin\\javaw.exe";
 static const wchar_t *const JRE_DOWNLOAD_LINK = L"https://adoptopenjdk.net/";
+static const size_t MIN_MUTEXID_LENGTH = 5U;
 static const DWORD SPLASH_SCREEN_TIMEOUT = 30000U;
 
 /* ======================================================================== */
@@ -918,6 +919,47 @@ static void show_jre_download_notice(const HWND hwnd, const wchar_t *const title
     }
 }
 
+/* ======================================================================== */
+/* Single instance                                                          */
+/* ======================================================================== */
+
+static ULONGLONG hash_code(const BYTE *const message, const size_t message_len)
+{
+    ULONGLONG hash = 0xCBF29CE484222325ull;
+    for (size_t iter = 0U; iter < message_len; ++iter)
+    {
+        hash ^= message[iter];
+        hash *= 0x00000100000001B3ull;
+    }
+    return hash;
+}
+
+static BOOL initialize_mutex(HANDLE *const handle, const wchar_t *const mutex_name)
+{
+    static const char *const BUILD_TIME = __DATE__ " " __TIME__;
+
+    const ULONGLONG hashcode_0 = hash_code((const BYTE*)BUILD_TIME, sizeof(wchar_t) * strlen(BUILD_TIME));
+    const ULONGLONG hashcode_1 = hash_code((const BYTE*)mutex_name, sizeof(wchar_t) * wcslen(mutex_name));
+
+    const wchar_t *const mutex_uuid = awprintf(L"l5j.%016llX%016llX", hashcode_0, hashcode_1);
+    if (!mutex_uuid)
+    {
+        return TRUE; /*better safe than sorry*/
+    }
+
+    BOOL result = TRUE;
+    if ((*handle = CreateMutexW(NULL, TRUE, mutex_uuid)) != NULL)
+    {
+        if (GetLastError() == ERROR_ALREADY_EXISTS)
+        {
+            result = FALSE;
+        }
+    }
+
+    free((void*)mutex_uuid);
+    return result;
+}
+
 /* ======================================================================== */
 /* Utilities                                                                */
 /* ======================================================================== */
@@ -959,7 +1001,8 @@ static wchar_t *const DEFAULT_HEADING = L"Launch5j";
 int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PWSTR pCmdLine, int nCmdShow)
 {
     int result = -1;
-    const wchar_t *app_heading = NULL, *executable_path = NULL, *executable_directory = NULL, *jarfile_path = NULL, *java_runtime_path = NULL, *jvm_extra_args = NULL, *cmd_extra_args = NULL, *command_line = NULL;
+    const wchar_t *app_heading = NULL, *mutex_name = NULL, *executable_path = NULL, *executable_directory = NULL, *jarfile_path = NULL, *java_runtime_path = NULL, *jvm_extra_args = NULL, *cmd_extra_args = NULL, *command_line = NULL;
+    HANDLE mutex_handle = NULL;
     DWORD java_required_bitness = 0U;
     ULONGLONG java_required_ver_min = 0ULL, java_required_ver_max = 0ULL;
     HGDIOBJ splash_image = NULL;
@@ -976,6 +1019,21 @@ int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PWSTR pCmdLine
     // Create the window
     HWND hwnd = CreateWindowExW(WS_EX_TOOLWINDOW | WS_EX_TOPMOST, L"STATIC", APP_HEADING, WS_POPUP | SS_BITMAP, 0, 0, CW_USEDEFAULT, CW_USEDEFAULT, NULL, NULL, hInstance, NULL);
 
+    // Single instance
+    mutex_name = load_string(hInstance, ID_STR_MUTEXID);
+    if (AVAILABLE(mutex_name) && (wcslen(mutex_name) >= MIN_MUTEXID_LENGTH + ((mutex_name[0U] == L'@') ? 0U : 1U)))
+    {
+        if(!initialize_mutex(&mutex_handle, (mutex_name[0U] == L'@') ? mutex_name + 1U : mutex_name))
+        {
+            if(mutex_name[0U] != L'@')
+            {
+                show_message(hwnd, MB_ICONWARNING | MB_TOPMOST, APP_HEADING, L"The application is already running.\n\n"
+                    L"If you see this message even though the application does not appear to be running, try restarting your computer!");
+            }
+            goto cleanup;
+        }
+    }
+
     // Show the splash screen
 #if ENABLE_SPLASH
     if (splash_image = LoadImage(hInstance, MAKEINTRESOURCE(ID_BITMAP_SPLASH), IMAGE_BITMAP, 0, 0, LR_DEFAULTSIZE))
@@ -1113,6 +1171,7 @@ cleanup:
 
     close_handle(&process_info.hThread);
     close_handle(&process_info.hProcess);
+    close_handle(&mutex_handle);
 
     destroy_window(&hwnd);
     delete_object(&splash_image);
@@ -1124,6 +1183,7 @@ cleanup:
     free((void*)jarfile_path);
     free((void*)executable_directory);
     free((void*)executable_path);
+    free((void*)mutex_name);
     free((void*)app_heading);
 
     return result;
diff --git a/src/resource.h b/src/resource.h
index 5a8a4e6..0539073 100644
--- a/src/resource.h
+++ b/src/resource.h
@@ -24,3 +24,4 @@
 #define ID_STR_JAVAMIN 4
 #define ID_STR_JAVAMAX 5
 #define ID_STR_BITNESS 6
+#define ID_STR_MUTEXID 7