diff --git a/manifest b/manifest
index 0e1b742f45..21ebfe0326 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Enhance\sthe\sformat()\sfunction\sso\sthat\sthe\s","\smodifier\sworks\sfor\sfloating\npoint\snumbers\sin\saddition\sto\sintegers.
-D 2023-05-04T14:44:53.844
+C Add\sthe\s"subsecond"\smodifier\sto\sthe\sdate/time\sfunctions.
+D 2023-05-04T20:28:19.528
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -581,7 +581,7 @@ F src/build.c 8357d6ca9a8c9afc297c431df28bc2af407b47f3ef2311875276c944b30c4d54
 F src/callback.c 4cd7225b26a97f7de5fee5ae10464bed5a78f2adefe19534cc2095b3a8ca484a
 F src/complete.c a3634ab1e687055cd002e11b8f43eb75c17da23e
 F src/ctime.c 20507cc0b0a6c19cd882fcd0eaeda32ae6a4229fb4b024cfdf3183043d9b703d
-F src/date.c f21815ca7172ce073db3163ac54c8d9f2841077165c1a6123b4d1c376a0c7ec7
+F src/date.c aca9e0c08b400b21238b609aea7c09585396cd770985cf8f475560f69222dad3
 F src/dbpage.c f3eea5f7ec47e09ee7da40f42b25092ecbe961fc59566b8e5f705f34335b2387
 F src/dbstat.c ec92074baa61d883de58c945162d9e666c13cd7cf3a23bc38b4d1c4d0b2c2bef
 F src/delete.c a9c6d3f51c0a31e9b831e0a0580a98d702904b42d216fee530940e40dec34873
@@ -925,7 +925,7 @@ F test/ctime.test 340f362f41f92972bbd71f44e10569a5cc694062b692231bd08aa6fe6c1c47
 F test/cursorhint.test 05cf0febe5c5f8a31f199401fd1c9322249e753950d55f26f9d5aca61408a270
 F test/cursorhint2.test 6f3aa9cb19e7418967a10ec6905209bcbb5968054da855fc36c8beee9ae9c42f
 F test/dataversion1.test 6e5e86ac681f0782e766ebcb56c019ae001522d114e0e111e5ebf68ccf2a7bb8
-F test/date.test 118e04db8c8b4efeb885542b4918c7b869a34c460a6bebbfe927dfd75706b80d
+F test/date.test 1d44557f668298b10d3335b22ab8feb133267b67ec4d85538908fe4dfebd2611
 F test/date2.test 7e12ec14aaf4d5e6294b4ba140445b0eca06ea50062a9c3a69c4ee13d0b6f8b1
 F test/date3.test a1b77abf05c6772fe5ca2337cac1398892f2a41e62bce7e6be0f4a08a0e64ae5
 F test/dbdata.test 042f49acff3438f940eeba5868d3af080ae64ddf26ae78f80c92bec3ca7d8603
@@ -2068,9 +2068,9 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P d3370d59cffb7ab982d6c620c93d22aa6a9dc786e1c4af95ca8d45ff0b9b7d6f 7080e196a1f887640ff51ddc508ec6796ce12874c2944855702753b64a8e5e50
-R ba5de07dbdc63490b9fe4eac9a9617b8
-T +closed 7080e196a1f887640ff51ddc508ec6796ce12874c2944855702753b64a8e5e50
+P 83683e108bce83c105bbcce1aa62880d8f14ebf3383d87d83a1e5c85026a7817 6499ebff545e663198bd0534be205a4e9ca68c7fb20fdcfa54fae4d9b79bfe3a
+R 8af27f80731782e09fcf7d27c983e6a4
+T +closed 6499ebff545e663198bd0534be205a4e9ca68c7fb20fdcfa54fae4d9b79bfe3a
 U drh
-Z f040165d56f687ae5af07ee029ea9c36
+Z ec3e442191ef8c8a1600e49b9abb536f
 # Remove this line to create a well-formed Fossil manifest.
diff --git a/manifest.uuid b/manifest.uuid
index 7846920bc7..54e7dbe993 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-83683e108bce83c105bbcce1aa62880d8f14ebf3383d87d83a1e5c85026a7817
\ No newline at end of file
+6fcb5a941fba0449d017954590bde7da74e5a1f8fd9b3e1febdff9bed1f22051
\ No newline at end of file
diff --git a/src/date.c b/src/date.c
index 7cc6fa684e..9b7957bbf0 100644
--- a/src/date.c
+++ b/src/date.c
@@ -77,6 +77,7 @@ struct DateTime {
   char validTZ;       /* True (1) if tz is valid */
   char tzSet;         /* Timezone was set explicitly */
   char isError;       /* An overflow has occurred */
+  char useSubsec;     /* Display subsecond precision */
 };
 
 
@@ -391,6 +392,11 @@ static int parseDateOrTime(
   }else if( sqlite3AtoF(zDate, &r, sqlite3Strlen30(zDate), SQLITE_UTF8)>0 ){
     setRawDateNumber(p, r);
     return 0;
+  }else if( (sqlite3StrICmp(zDate,"subsec")==0
+             || sqlite3StrICmp(zDate,"subsecond")==0)
+           && sqlite3NotPureFunc(context) ){
+    p->useSubsec = 1;
+    return setDateTimeToCurrent(context, p);
   }
   return 1;
 }
@@ -805,8 +811,22 @@ static int parseModifier(
       **
       ** Move the date backwards to the beginning of the current day,
       ** or month or year.
+      **
+      **    subsecond
+      **    subsec
+      **
+      ** Show subsecond precision in the output of datetime() and
+      ** unixepoch() and strftime('%s').
       */
-      if( sqlite3_strnicmp(z, "start of ", 9)!=0 ) break;
+      if( sqlite3_strnicmp(z, "start of ", 9)!=0 ){
+        if( sqlite3_stricmp(z, "subsec")==0
+         || sqlite3_stricmp(z, "subsecond")==0
+        ){
+          p->useSubsec = 1;
+          rc = 0;
+        }
+        break;
+      }        
       if( !p->validJD && !p->validYMD && !p->validHMS ) break;
       z += 9;
       computeYMD(p);
@@ -1004,7 +1024,11 @@ static void unixepochFunc(
   DateTime x;
   if( isDate(context, argc, argv, &x)==0 ){
     computeJD(&x);
-    sqlite3_result_int64(context, x.iJD/1000 - 21086676*(i64)10000);
+    if( x.useSubsec ){
+      sqlite3_result_double(context, (x.iJD - 21086676*(i64)10000000)/1000.0);
+    }else{
+      sqlite3_result_int64(context, x.iJD/1000 - 21086676*(i64)10000);
+    }
   }
 }
 
@@ -1020,8 +1044,8 @@ static void datetimeFunc(
 ){
   DateTime x;
   if( isDate(context, argc, argv, &x)==0 ){
-    int Y, s;
-    char zBuf[24];
+    int Y, s, n;
+    char zBuf[32];
     computeYMD_HMS(&x);
     Y = x.Y;
     if( Y<0 ) Y = -Y;
@@ -1042,15 +1066,28 @@ static void datetimeFunc(
     zBuf[15] = '0' + (x.m/10)%10;
     zBuf[16] = '0' + (x.m)%10;
     zBuf[17] = ':';
-    s = (int)x.s;
-    zBuf[18] = '0' + (s/10)%10;
-    zBuf[19] = '0' + (s)%10;
-    zBuf[20] = 0;
+    if( x.useSubsec ){
+      s = (int)1000.0*x.s;
+      zBuf[18] = '0' + (s/10000)%10;
+      zBuf[19] = '0' + (s/1000)%10;
+      zBuf[20] = '.';
+      zBuf[21] = '0' + (s/100)%10;
+      zBuf[22] = '0' + (s/10)%10;
+      zBuf[23] = '0' + (s)%10;
+      zBuf[24] = 0;
+      n = 24;
+    }else{
+      s = (int)x.s;
+      zBuf[18] = '0' + (s/10)%10;
+      zBuf[19] = '0' + (s)%10;
+      zBuf[20] = 0;
+      n = 20;
+    }
     if( x.Y<0 ){
       zBuf[0] = '-';
-      sqlite3_result_text(context, zBuf, 20, SQLITE_TRANSIENT);
+      sqlite3_result_text(context, zBuf, n, SQLITE_TRANSIENT);
     }else{
-      sqlite3_result_text(context, &zBuf[1], 19, SQLITE_TRANSIENT);
+      sqlite3_result_text(context, &zBuf[1], n-1, SQLITE_TRANSIENT);
     }
   }
 }
@@ -1067,7 +1104,7 @@ static void timeFunc(
 ){
   DateTime x;
   if( isDate(context, argc, argv, &x)==0 ){
-    int s;
+    int s, n;
     char zBuf[16];
     computeHMS(&x);
     zBuf[0] = '0' + (x.h/10)%10;
@@ -1076,11 +1113,24 @@ static void timeFunc(
     zBuf[3] = '0' + (x.m/10)%10;
     zBuf[4] = '0' + (x.m)%10;
     zBuf[5] = ':';
-    s = (int)x.s;
-    zBuf[6] = '0' + (s/10)%10;
-    zBuf[7] = '0' + (s)%10;
-    zBuf[8] = 0;
-    sqlite3_result_text(context, zBuf, 8, SQLITE_TRANSIENT);
+    if( x.useSubsec ){
+      s = (int)1000.0*x.s;
+      zBuf[6] = '0' + (s/10000)%10;
+      zBuf[7] = '0' + (s/1000)%10;
+      zBuf[8] = '.';
+      zBuf[9] = '0' + (s/100)%10;
+      zBuf[10] = '0' + (s/10)%10;
+      zBuf[11] = '0' + (s)%10;
+      zBuf[12] = 0;
+      n = 12;
+    }else{
+      s = (int)x.s;
+      zBuf[6] = '0' + (s/10)%10;
+      zBuf[7] = '0' + (s)%10;
+      zBuf[8] = 0;
+      n = 8;
+    }
+    sqlite3_result_text(context, zBuf, n, SQLITE_TRANSIENT);
   }
 }
 
@@ -1211,8 +1261,13 @@ static void strftimeFunc(
         break;
       }
       case 's': {
-        i64 iS = (i64)(x.iJD/1000 - 21086676*(i64)10000);
-        sqlite3_str_appendf(&sRes,"%lld",iS);
+        if( x.useSubsec ){
+          sqlite3_str_appendf(&sRes,"%.3f",
+                (x.iJD - 21086676*(i64)10000000)/1000.0);
+        }else{
+          i64 iS = (i64)(x.iJD/1000 - 21086676*(i64)10000);
+          sqlite3_str_appendf(&sRes,"%lld",iS);
+        }
         break;
       }
       case 'S': {
diff --git a/test/date.test b/test/date.test
index 62233ad8f6..3e93181896 100644
--- a/test/date.test
+++ b/test/date.test
@@ -544,4 +544,10 @@ datetest 17.7 {datetime(38,'start of year')} {-4712-01-01 00:00:00}
 #
 datetest 18.1 {strftime('%f',1.234,'unixepoch','localtime')} {01.234}
 
+# 2023-04 The 'subsecond' (or 'subsec') modifier alters resolutions
+# to at least milliseconds. Added for release 3.42.0 .
+datetest 18.2 {unixepoch('1970-01-01T00:00:00.1', 'subsec')} {0.1}
+datetest 18.3 {unixepoch('1970-01-01T00:00:00.2', 'subsecond')} {0.2}
+datetest 18.4 {julianday('-4713-11-24 13:40:48.864', 'subsec')} {0.07001}
+datetest 18.5 {typeof(unixepoch('now', 'subsecond'))} {real}
 finish_test