diff --git a/lib/std/core/builtin.c3 b/lib/std/core/builtin.c3
index b5d88304a..8833e690f 100644
--- a/lib/std/core/builtin.c3
+++ b/lib/std/core/builtin.c3
@@ -57,6 +57,10 @@ faultdef TYPE_MISMATCH @builtin;
  Use `CAPACITY_EXCEEDED` when trying to add to a bounded list or similar.
 */
 faultdef CAPACITY_EXCEEDED @builtin;
+/*
+ Use `NOT_IMPLEMENTED` when something is conditionally available.
+*/
+faultdef NOT_IMPLEMENTED @builtin;
 
 alias VoidFn = fn void();
 
diff --git a/lib/std/core/logging.c3 b/lib/std/core/logging.c3
new file mode 100644
index 000000000..bccf09361
--- /dev/null
+++ b/lib/std/core/logging.c3
@@ -0,0 +1,217 @@
+module std::core::log;
+import std::io, std::thread, std::time, std::math::random;
+
+const FULL_LOG = env::COMPILER_SAFE_MODE || $feature(FULL_LOG);
+
+typedef LogCategory = inline char;
+typedef LogTag = char[12];
+
+const LogCategory CATEGORY_APPLICATION  = 0;
+const LogCategory CATEGORY_SYSTEM       = 1;
+const LogCategory CATEGORY_KERNEL       = 2;
+const LogCategory CATEGORY_AUDIO        = 3;
+const LogCategory CATEGORY_VIDEO        = 4;
+const LogCategory CATEGORY_RENDER       = 5;
+const LogCategory CATEGORY_INPUT        = 6;
+const LogCategory CATEGORY_NETWORK      = 7;
+const LogCategory CATEGORY_SOCKET       = 8;
+const LogCategory CATEGORY_SECURITY     = 9;
+const LogCategory CATEGORY_TEST         = 10;
+const LogCategory CATEGORY_ERROR        = 11;
+const LogCategory CATEGORY_ASSERT       = 12;
+const LogCategory CATEGORY_CRASH        = 13;
+const LogCategory CATEGORY_STATS        = 14;
+const LogCategory CATEGORY_CUSTOM_START = 100;
+
+tlocal LogCategory default_category = CATEGORY_APPLICATION;
+tlocal LogTag current_tag;
+
+
+enum LogPriority : int
+{
+	VERBOSE,
+	DEBUG,
+	INFO,
+	WARN,
+	ERROR,
+	CRITICAL,
+}
+
+interface Logger
+{
+	fn void log(LogPriority priority, LogCategory category, LogTag tag, String file, String function, int line, String fmt, any[] args);
+}
+
+macro void verbose(String fmt, ..., LogCategory category = default_category) => call_log(VERBOSE, category, fmt, $vasplat);
+macro void debug(String fmt, ..., LogCategory category = default_category) => call_log(DEBUG, category, fmt, $vasplat);
+macro void info(String fmt, ..., LogCategory category = default_category) => call_log(INFO, category, fmt, $vasplat);
+macro void warn(String fmt, ..., LogCategory category = default_category) => call_log(WARN, category, fmt, $vasplat);
+macro void error(String fmt, ..., LogCategory category = default_category) => call_log(ERROR, category, fmt, $vasplat);
+macro void critical(String fmt, ..., LogCategory category = default_category) => call_log(CRITICAL, category, fmt, $vasplat);
+
+macro void @category_scope(LogCategory new_category; @body)
+{
+	LogCategory old = default_category;
+	default_category = new_category;
+	defer default_category = old;
+	@body();
+}
+
+<*
+ @require tag_prefix.len <= 3 : "The prefix may not exceed 3 bytes"
+*>
+macro void @tag_scope(String tag_prefix = ""; @body)
+{
+	LogTag old = current_tag;
+	push_tag(tag_prefix);
+	defer current_tag = old;
+	@body();
+}
+
+<*
+ @require tag_prefix.len <= 3 : "The prefix may not exceed 3 bytes"
+*>
+macro void push_tag(String tag_prefix = "")
+{
+	current_tag = create_tag(tag_prefix);
+}
+
+<*
+ @require tag_prefix.len <= 3 : "The prefix may not exceed 3 bytes"
+*>
+fn LogTag create_tag(String tag_prefix)
+{
+	LogTag tag @noinit;
+	int start = 0;
+	foreach (int i, c : tag_prefix)
+	{
+		if (c == 0) break;
+		tag[start++] = c;
+	}
+	if (start > 0) tag[start++] = '_';
+	for (int i = start; i < tag.len; i++)
+	{
+		tag[i] = (char)rand_in_range('a', 'z');
+	}
+	return tag;
+}
+
+fn void set_priority_for_category(LogCategory category, LogPriority new_priority)
+{
+	@atomic_store(config_priorities[category], new_priority, UNORDERED);
+}
+
+fn LogPriority get_priority_for_category(LogCategory category)
+{
+	return @atomic_load(config_priorities[category], UNORDERED);
+}
+
+fn void set_priority_all(LogPriority new_priority)
+{
+	for (int i = 0; i < config_priorities.len; i++)
+	{
+		@atomic_store(config_priorities[i], new_priority, UNORDERED);
+	}
+}
+fn void set_logger(Logger logger)
+{
+	init();
+	if (!logger_mutex.is_initialized())
+	{
+		current_logger = logger;
+		current_logfn = &logger.log;
+		return;
+	}
+	logger_mutex.@in_lock()
+	{
+		current_logger = logger;
+		current_logfn = &logger.log;
+	};
+}
+
+macro void init()
+{
+	log_init.call(fn () => (void)logger_mutex.init());
+}
+
+fn void call_log(LogPriority prio, LogCategory category, String fmt, args...)
+{
+	LogPriority priority = mem::@atomic_load(config_priorities[category], UNORDERED);
+	if (priority < prio) return;
+	init();
+	bool locked = logger_mutex.is_initialized() && @ok(logger_mutex.lock());
+	Logger logger = current_logger;
+	LogFn logfn = current_logfn;
+	defer if (locked) (void)logger_mutex.unlock();
+	$if FULL_LOG:
+	logfn(logger.ptr, prio, category, current_tag, $$FILE, $$FUNC, $$LINE, fmt, args);
+	$else
+	logfn(logger.ptr, prio, category, current_tag, "", "", 0, fmt, args);
+	$endif
+}
+
+fn String? get_category_name(LogCategory category)
+{
+	String val = category_names[category];
+	return val ?: NOT_FOUND?;
+}
+
+fn void set_category_name(LogCategory category, String name)
+{
+	category_names[category] = name;
+}
+
+struct NullLogger (Logger)
+{
+	void* dummy;
+}
+
+fn void NullLogger.log(&self, LogPriority priority, LogCategory category, LogTag tag, String file, String function, int line, String fmt, any[] args) @dynamic
+{}
+
+
+module std::core::log @private;
+import std::io, std::thread, std::time;
+
+struct StderrLogger (Logger) @if(env::LIBC)
+{
+	void* dummy;
+}
+
+fn void StderrLogger.log(&self, LogPriority priority, LogCategory category, LogTag tag, String file, String function, int line, String fmt, any[] args) @dynamic @if(env::LIBC)
+{
+	@stack_mem(256 + 64; Allocator mem)
+	{
+		DString str;
+		str.init(mem, 256);
+		str.appendf(fmt, ...args);
+		TzDateTime time = datetime::now().to_local();
+		io::eprintfn("[%02d:%02d:%02d:%04d] [%s] %s", time.hour, time.min, time.sec, (time.usec / 1000), priority, str);
+	};
+}
+
+alias LogFn = fn void(void*, LogPriority priority, LogCategory category, LogTag tag, String file, String function, int line, String fmt, any[] args);
+LogFn current_logfn = @select(env::LIBC, (LogFn)&StderrLogger.log, (LogFn)&NullLogger.log);
+OnceFlag log_init;
+Mutex logger_mutex;
+Logger current_logger = @select(env::LIBC, &stderr_logger, &null_logger);
+StderrLogger stderr_logger @if (env::LIBC);
+NullLogger null_logger;
+LogPriority[256] config_priorities = { [0..255] = ERROR, [CATEGORY_APPLICATION] = INFO, [CATEGORY_TEST] = VERBOSE, [CATEGORY_ASSERT] = WARN};
+String[256] category_names = {
+	[CATEGORY_APPLICATION] = "APP",
+    [CATEGORY_SYSTEM] = "SYSTEM",
+    [CATEGORY_KERNEL] = "KERNEL",
+    [CATEGORY_AUDIO] = "AUDIO",
+    [CATEGORY_VIDEO] = "VIDEO",
+    [CATEGORY_RENDER] = "RENDER",
+    [CATEGORY_INPUT] = "INPUT",
+    [CATEGORY_NETWORK] = "NETWORD",
+    [CATEGORY_SOCKET] = "SOCKET",
+    [CATEGORY_SECURITY] = "SECURITY",
+    [CATEGORY_TEST] = "TEST",
+    [CATEGORY_ERROR] = "ERROR",
+    [CATEGORY_ASSERT] = "ASSERT",
+    [CATEGORY_CRASH] = "CRASH",
+    [CATEGORY_STATS] = "STATS"
+};
diff --git a/lib/std/io/io.c3 b/lib/std/io/io.c3
index b48f4fddd..b0d0daaa4 100644
--- a/lib/std/io/io.c3
+++ b/lib/std/io/io.c3
@@ -254,7 +254,7 @@ macro void eprint(x)
 
  @param x : "The value to print"
 *>
-macro void eprintn(x)
+macro void eprintn(x = "")
 {
 	(void)fprintn(io::stderr(), x);
 }
diff --git a/lib/std/threads/os/thread_none.c3 b/lib/std/threads/os/thread_none.c3
index 3509433a2..9148d58e5 100644
--- a/lib/std/threads/os/thread_none.c3
+++ b/lib/std/threads/os/thread_none.c3
@@ -4,4 +4,24 @@ typedef NativeMutex = int;
 typedef NativeTimedMutex = int;
 typedef NativeConditionVariable = int;
 typedef NativeOnceFlag = int;
-typedef NativeThread = int;
\ No newline at end of file
+typedef NativeThread = int;
+
+fn void NativeOnceFlag.call_once(&flag, OnceFn func)
+{
+	if (*flag == 0)
+	{
+		*flag = 1;
+		func();
+	}
+}
+
+fn void? NativeMutex.init(&mtx, MutexType type) => NOT_IMPLEMENTED?;
+
+fn bool NativeMutex.is_initialized(&self)
+{
+	return false;
+}
+
+macro void? NativeMutex.lock(&mutex) => NOT_IMPLEMENTED?;
+macro bool NativeMutex.try_lock(&mutex) => NOT_IMPLEMENTED?;
+macro void? NativeMutex.unlock(&mutex) => NOT_IMPLEMENTED?;
\ No newline at end of file
diff --git a/lib/std/threads/os/thread_win32.c3 b/lib/std/threads/os/thread_win32.c3
index a3f0cfc05..45107ee2d 100644
--- a/lib/std/threads/os/thread_win32.c3
+++ b/lib/std/threads/os/thread_win32.c3
@@ -15,6 +15,11 @@ struct NativeMutex
 	}
 }
 
+fn bool NativeMutex.is_initialized(&self)
+{
+	return self.initialized;
+}
+
 struct NativeTimedMutex
 {
 	Win32_SRWLOCK srw_lock;
diff --git a/lib/std/threads/thread.c3 b/lib/std/threads/thread.c3
index 5103f18ec..693dd8ef6 100644
--- a/lib/std/threads/thread.c3
+++ b/lib/std/threads/thread.c3
@@ -34,6 +34,7 @@ faultdef
 	CHANNEL_CLOSED;
 
 macro void? Mutex.init(&mutex) => NativeMutex.init((NativeMutex*)mutex, {});
+macro bool Mutex.is_initialized(mutex) => ((NativeMutex*)&mutex).is_initialized();
 macro void? RecursiveMutex.init(&mutex) => NativeMutex.init((NativeMutex*)mutex, {.recursive});
 macro void? Mutex.destroy(&mutex) => NativeMutex.destroy((NativeMutex*)mutex);
 macro void? Mutex.lock(&mutex) => NativeMutex.lock((NativeMutex*)mutex);
diff --git a/releasenotes.md b/releasenotes.md
index db609263b..db57d140f 100644
--- a/releasenotes.md
+++ b/releasenotes.md
@@ -26,6 +26,7 @@
 - Add `vm::mmap_file` to memory map a file.
 - Updated hash functions in default hash methods.
 - Added `FixedBlockPool` which is a memory pool for fixed size blocks.
+- Added the experimental `std::core::log` for logging.
 
 ## 0.7.4 Change list
 
diff --git a/test/test_suite/stdlib/logging.c3t b/test/test_suite/stdlib/logging.c3t
new file mode 100644
index 000000000..5e86048ea
--- /dev/null
+++ b/test/test_suite/stdlib/logging.c3t
@@ -0,0 +1,54 @@
+// #target: macos-x64
+module test;
+import std;
+
+fn void main()
+{
+	log::@category_scope(log::CATEGORY_KERNEL)
+	{
+		log::@tag_scope("YO")
+		{
+			log::info("Hello");
+		};
+	};
+}
+
+/* #expect: test.ll
+
+define void @test.main() #0 {
+entry:
+  %old = alloca i8, align 1
+  %old1 = alloca [12 x i8], align 1
+  %result = alloca [12 x i8], align 1
+  %tempcoerce = alloca { i64, i32 }, align 8
+  %category = alloca i8, align 1
+  %0 = call ptr @llvm.threadlocal.address.p0(ptr @std.core.log.default_category)
+  %1 = load i8, ptr %0, align 1
+  store i8 %1, ptr %old, align 1
+  %2 = call ptr @llvm.threadlocal.address.p0(ptr @std.core.log.default_category)
+  store i8 2, ptr %2, align 1
+  call void @llvm.assume(i1 true)
+  %3 = call ptr @llvm.threadlocal.address.p0(ptr @std.core.log.current_tag)
+  call void @llvm.memcpy.p0.p0.i32(ptr align 1 %old1, ptr align 1 %3, i32 12, i1 false)
+  call void @llvm.assume(i1 true)
+  %4 = call ptr @llvm.threadlocal.address.p0(ptr @std.core.log.current_tag)
+  %5 = call { i64, i32 } @std.core.log.create_tag(ptr @.str, i64 2)
+  store { i64, i32 } %5, ptr %tempcoerce, align 8
+  call void @llvm.memcpy.p0.p0.i32(ptr align 1 %result, ptr align 8 %tempcoerce, i32 12, i1 false)
+  call void @llvm.memcpy.p0.p0.i32(ptr align 1 %4, ptr align 1 %result, i32 12, i1 false)
+  %6 = call ptr @llvm.threadlocal.address.p0(ptr @std.core.log.default_category)
+  %7 = load i8, ptr %6, align 1
+  store i8 %7, ptr %category, align 1
+  %8 = load i8, ptr %category, align 1
+  call void @std.core.log.call_log(i32 2, i8 zeroext %8, ptr @.str.1, i64 5, ptr null, i64 0)
+  %9 = call ptr @llvm.threadlocal.address.p0(ptr @std.core.log.current_tag)
+  call void @llvm.memcpy.p0.p0.i32(ptr align 1 %9, ptr align 1 %old1, i32 12, i1 false)
+  %10 = call ptr @llvm.threadlocal.address.p0(ptr @std.core.log.default_category)
+  %11 = load i8, ptr %old, align 1
+  store i8 %11, ptr %10, align 1
+  ret void
+}
+
+declare extern_weak { i64, i32 } @std.core.log.create_tag(ptr, i64) #0
+
+declare extern_weak void @std.core.log.call_log(i32, i8 zeroext, ptr, i64, ptr, i64) #0