Index: src/main.c
==================================================================
--- src/main.c
+++ src/main.c
@@ -2965,8 +2965,22 @@
   while( zFilename[0] ){
     int x = strcmp(zFilename, zParam);
     zFilename += sqlite3Strlen30(zFilename) + 1;
     if( x==0 ) return zFilename;
     zFilename += sqlite3Strlen30(zFilename) + 1;
+  }
+  return 0;
+}
+
+/*
+** Return the filename of the database associated with a database
+** connection.
+*/
+const char *sqlite3_db_filename(sqlite3 *db, const char *zDbName){
+  int i;
+  for(i=0; i<db->nDb; i++){
+    if( db->aDb[i].pBt && sqlite3StrICmp(zDbName, db->aDb[i].zName)==0 ){
+      return sqlite3BtreeGetFilename(db->aDb[i].pBt);
+    }
   }
   return 0;
 }

Index: src/sqlite.h.in
==================================================================
--- src/sqlite.h.in
+++ src/sqlite.h.in
@@ -4371,10 +4371,21 @@
 ** to the [sqlite3_prepare_v2()] call (or its variants) that was used to
 ** create the statement in the first place.
 */
 sqlite3 *sqlite3_db_handle(sqlite3_stmt*);
 
+/*
+** CAPI3REF: Return The Filename For A Database Connection
+**
+** ^The sqlite3_db_filename(D,N) interface returns a pointer to a filename
+** associated with database N of connection D.  ^The main database file
+** has the name "main".  If there is no attached database N on the database
+** connection D, or if database N is a temporary or in-memory database, then
+** a NULL pointer is returned.
+*/
+const char *sqlite3_db_filename(sqlite3 *db, const char *zDbName);
+
 /*
 ** CAPI3REF: Find the next prepared statement
 **
 ** ^This interface returns a pointer to the next [prepared statement] after
 ** pStmt associated with the [database connection] pDb.  ^If pStmt is NULL

Index: src/test1.c
==================================================================
--- src/test1.c
+++ src/test1.c
@@ -4615,10 +4615,33 @@
   if( getDbPointer(interp, Tcl_GetString(objv[1]), &db) ) return TCL_ERROR;
   rc = sqlite3_db_release_memory(db);
   Tcl_SetObjResult(interp, Tcl_NewIntObj(rc));
   return TCL_OK;
 }
+
+/*
+** Usage:  sqlite3_db_filename DB DBNAME
+**
+** Return the name of a file associated with a database.
+*/
+static int test_db_filename(
+  void * clientData,
+  Tcl_Interp *interp,
+  int objc,
+  Tcl_Obj *CONST objv[]
+){
+  sqlite3 *db;
+  const char *zDbName;
+  if( objc!=3 ){
+    Tcl_WrongNumArgs(interp, 1, objv, "DB DBNAME");
+    return TCL_ERROR;
+  }
+  if( getDbPointer(interp, Tcl_GetString(objv[1]), &db) ) return TCL_ERROR;
+  zDbName = Tcl_GetString(objv[2]);
+  Tcl_AppendResult(interp, sqlite3_db_filename(db, zDbName), (void*)0);
+  return TCL_OK;
+}
 
 /*
 ** Usage:  sqlite3_soft_heap_limit ?N?
 **
 ** Query or set the soft heap limit for the current thread.  The
@@ -5939,10 +5962,11 @@
      { "sqlite3_stmt_readonly",         test_stmt_readonly ,0 },
      { "uses_stmt_journal",             uses_stmt_journal ,0 },
 
      { "sqlite3_release_memory",        test_release_memory,     0},
      { "sqlite3_db_release_memory",     test_db_release_memory,  0},
+     { "sqlite3_db_filename",           test_db_filename,        0},
      { "sqlite3_soft_heap_limit",       test_soft_heap_limit,    0},
      { "sqlite3_thread_cleanup",        test_thread_cleanup,     0},
      { "sqlite3_pager_refcounts",       test_pager_refcounts,    0},
 
      { "sqlite3_load_extension",        test_load_extension,     0},

Index: test/attach.test
==================================================================
--- test/attach.test
+++ test/attach.test
@@ -49,10 +49,29 @@
   execsql {
     ATTACH DATABASE 'test2.db' AS two;
     SELECT * FROM two.t2;
   }
 } {1 x 2 y}
+
+# Tests for the sqlite3_db_filename interface
+#
+do_test attach-1.3.1 {
+  file tail [sqlite3_db_filename db main]
+} {test.db}
+do_test attach-1.3.2 {
+  file tail [sqlite3_db_filename db MAIN]
+} {test.db}
+do_test attach-1.3.3 {
+  file tail [sqlite3_db_filename db temp]
+} {}
+do_test attach-1.3.4 {
+  file tail [sqlite3_db_filename db two]
+} {test2.db}
+do_test attach-1.3.5 {
+  file tail [sqlite3_db_filename db three]
+} {}
+
 do_test attach-1.4 {
   execsql {
     SELECT * FROM t2;
   }
 } {1 x 2 y}