diff --git a/src/MacVim/MMAppController.m b/src/MacVim/MMAppController.m
index be710e5f91..0e108ca5a9 100644
--- a/src/MacVim/MMAppController.m
+++ b/src/MacVim/MMAppController.m
@@ -153,6 +153,12 @@ fsEventCallback(ConstFSEventStreamRef streamRef,
 
 + (void)initialize
 {
+    static BOOL initDone = NO;
+    if (initDone) return;
+    initDone = YES;
+
+    ASLInit();
+
     NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:
         [NSNumber numberWithBool:NO],   MMNoWindowKey,
         [NSNumber numberWithInt:64],    MMTabMinWidthKey,
diff --git a/src/MacVim/MacVim.h b/src/MacVim/MacVim.h
index 895b4b98ad..68c74a4a6f 100644
--- a/src/MacVim/MacVim.h
+++ b/src/MacVim/MacVim.h
@@ -9,6 +9,7 @@
  */
 
 #import <Cocoa/Cocoa.h>
+#import <asl.h>
 
 
 //
@@ -224,10 +225,18 @@ enum {
 NSString *debugStringForMessageQueue(NSArray *queue);
 
 
+// Shared user defaults (most user defaults are in Miscellaneous.h).
+// Contrary to the user defaults in Miscellaneous.h these defaults are not
+// intitialized to any default values.  That is, unless the user sets them
+// these keys will not be present in the user default database.
+extern NSString *MMLogLevelKey;
+extern NSString *MMLogToStdErrKey;
+
 // Argument used to stop MacVim from opening an empty window on startup
 // (techincally this is a user default but should not be used as such).
 extern NSString *MMNoWindowKey;
 
+
 // Vim pasteboard type (holds motion type + string)
 extern NSString *VimPBoardType;
 
@@ -284,3 +293,55 @@ typedef int NSInteger;
 typedef unsigned int NSUInteger;
 # endif
 #endif
+
+
+
+// Logging related functions and macros.
+//
+// This is a very simplistic logging facility built on top of ASL.  Two user
+// defaults allow for changing the local log filter level (MMLogLevel) and
+// whether logs should be sent to stderr (MMLogToStdErr).  (These user defaults
+// are only checked during startup.)  The default is to block level 6 (info)
+// and 7 (debug) logs and _not_ to send logs to stderr.  Apart from this
+// "syslog" (see "man syslog") can be used to modify the ASL filters (it is
+// currently not possible to change the local filter at runtime).  For example:
+//   Enable all logs to reach the ASL database (by default 'debug' and 'info'
+//   are filtered out, see "man syslogd"):
+//     $ sudo syslog -c syslogd -d
+//   Reset the ASL database filter:
+//     $ sudo syslog -c syslogd off
+//   Change the master filter to block logs less severe than errors:
+//     $ sudo syslog -c 0 -e
+//   Change per-process filter for running MacVim process to block logs less
+//   severe than warnings:
+//     $ syslog -c MacVim -w
+//
+// Note that there are four ASL filters:
+//   1) The ASL database filter (syslog -c syslogd ...)
+//   2) The master filter (syslog -c 0 ...)
+//   3) The per-process filter (syslog -c PID ...)
+//   4) The local filter (MMLogLevel)
+//
+// To view the logs, either use "Console.app" or the "syslog" command:
+//   $ syslog -w | grep Vim
+// To get the logs to show up in Xcode enable the MMLogToStdErr user default.
+
+extern int ASLogLevel;
+
+void ASLInit();
+
+#define ASLog(level, fmt, ...) \
+    if (level <= ASLogLevel) { \
+        asl_log(NULL, NULL, level, "%s@%d %s", \
+            __PRETTY_FUNCTION__, __LINE__, \
+            [[NSString stringWithFormat:fmt, ##__VA_ARGS__] UTF8String]); \
+    }
+
+// Note: These macros are used like ASLogErr(@"text num=%d", 42).  Objective-C
+// style specifiers (%@) are supported.
+#define ASLogCrit(fmt, ...)   ASLog(ASL_LEVEL_CRIT,    fmt, ##__VA_ARGS__)
+#define ASLogErr(fmt, ...)    ASLog(ASL_LEVEL_ERR,     fmt, ##__VA_ARGS__)
+#define ASLogWarn(fmt, ...)   ASLog(ASL_LEVEL_WARNING, fmt, ##__VA_ARGS__)
+#define ASLogNotice(fmt, ...) ASLog(ASL_LEVEL_NOTICE,  fmt, ##__VA_ARGS__)
+#define ASLogInfo(fmt, ...)   ASLog(ASL_LEVEL_INFO,    fmt, ##__VA_ARGS__)
+#define ASLogDebug(fmt, ...)  ASLog(ASL_LEVEL_DEBUG,   fmt, ##__VA_ARGS__)
diff --git a/src/MacVim/MacVim.m b/src/MacVim/MacVim.m
index 058ce663d4..3e59d6b378 100644
--- a/src/MacVim/MacVim.m
+++ b/src/MacVim/MacVim.m
@@ -13,6 +13,7 @@
 
 #import "MacVim.h"
 
+
 char *MessageStrings[] = 
 {
     "INVALID MESSAGE ID",
@@ -99,6 +100,9 @@ char *MessageStrings[] =
 
 
 
+NSString *MMLogLevelKey     = @"MMLogLevel";
+NSString *MMLogToStdErrKey  = @"MMLogToStdErr";
+
 // Argument used to stop MacVim from opening an empty window on startup
 // (techincally this is a user default but should not be used as such).
 NSString *MMNoWindowKey = @"MMNoWindow";
@@ -106,6 +110,8 @@ NSString *MMNoWindowKey = @"MMNoWindow";
 // Vim pasteboard type (holds motion type + string)
 NSString *VimPBoardType = @"VimPBoardType";
 
+int ASLogLevel = ASL_LEVEL_NOTICE;
+
 
 
 // Create a string holding the labels of all messages in message queue for
@@ -244,3 +250,34 @@ debugStringForMessageQueue(NSArray *queue)
 }
 
 @end
+
+
+
+
+    void
+ASLInit()
+{
+    NSUserDefaults *ud = [NSUserDefaults standardUserDefaults];
+
+    // Allow for changing the log level via user defaults.  If no key is found
+    // the default log level will be used (which for ASL is to log everything
+    // up to ASL_LEVEL_NOTICE).  This key is an integer which corresponds to
+    // the ASL_LEVEL_* macros (0 is most severe, 7 is debug level).
+    id logLevelObj = [ud objectForKey:MMLogLevelKey];
+    if (logLevelObj) {
+        int logLevel = [logLevelObj intValue];
+        if (logLevel < 0) logLevel = 0;
+        if (logLevel > ASL_LEVEL_DEBUG) logLevel = ASL_LEVEL_DEBUG;
+
+        ASLogLevel = logLevel;
+        asl_set_filter(NULL, ASL_FILTER_MASK_UPTO(logLevel));
+    }
+
+    // Allow for changing whether a copy of each log should be sent to stderr
+    // (this defaults to NO if this key is missing in the user defaults
+    // database).  The above filter mask is applied to logs going to stderr,
+    // contrary to how "vanilla" ASL works.
+    BOOL logToStdErr = [ud boolForKey:MMLogToStdErrKey];
+    if (logToStdErr)
+        asl_add_log_file(NULL, 2);  // The file descriptor for stderr is 2
+}
diff --git a/src/MacVim/gui_macvim.m b/src/MacVim/gui_macvim.m
index 91ad7855de..86d332b3fa 100644
--- a/src/MacVim/gui_macvim.m
+++ b/src/MacVim/gui_macvim.m
@@ -42,6 +42,7 @@ vimmenu_T *menu_for_descriptor(NSArray *desc);
  * Parse the GUI related command-line arguments.  Any arguments used are
  * deleted from argv, and *argc is decremented accordingly.  This is called
  * when vim is started, whether or not the GUI has been started.
+ * NOTE: This function will be called twice if the Vim process forks.
  */
     void
 gui_mch_prepare(int *argc, char **argv)
@@ -110,6 +111,7 @@ gui_mch_init_check(void)
 gui_mch_init(void)
 {
     //NSLog(@"gui_mch_init()");
+    ASLInit();
 
     if (![[MMBackend sharedInstance] checkin]) {
         // TODO: Kill the process if there is no terminal to fall back on,