START

Start a specified program or command in a separate window.

Syntax
      START "title" [/Dpath] [options] "command" [parameters]

Key:
   title      : Text for the CMD window title bar (required)
   path       : Starting directory
   command    : The command, batch file or executable program to run
   parameters : The parameters passed to the command

Options:
   /MIN       : Minimized
   /MAX       : Maximized
   /WAIT      : Start application and wait for it to terminate
   /LOW       : Use IDLE priority class
   /NORMAL    : Use NORMAL priority class
   /HIGH      : Use HIGH priority class
   /REALTIME  : Use REALTIME priority class

   /B         : Start application without creating a new window. In this case
                ^C will be ignored - leaving ^Break as the only way to 
                interrupt the application
   /I         : Ignore any changes to the current environment.

   Options for 16-bit WINDOWS programs only

   /SEPARATE   Start in separate memory space (more robust)
   /SHARED     Start in shared memory space (default)

Notes:

Always include a TITLE this can be a simple string like "My Script" or just a pair of empty quotes ""
According to the Microsoft documentation, the title is optional, but you may have problems if it is omitted.

Document files may be invoked through their file association just by typing the name of the file as a command.
e.g. START "" WORD.DOC would launch the application associated with the .DOC file extension

Examples

START "My Login Script" /Min Login.cmd

START "" /wait MySlowProgram.exe

Printers
A new printer can be installed very quickly (and the driver downloaded) with the command:

START \\print_server\printer_name

Setting a Working Directory
To start an application and specify where files will be saved:

START /Dc:\Documents\ /MAX notepad.exe

Note that START /D does not support long filenames which contain spaces, a workaround is to use the 8.3 compatible name(s)

Forcing a Sequence of Programs
If you require your users to run a sequence of 32 bit GUI programs to complete a task, create a batch file that uses the start command:

@echo off
start /wait /b First.exe
start /wait /b Second.exe
start /wait /b Third.exe

Create a shortcut to this batch file and place it on the Start menu or desktop. Set it to run minimized.
When the user double-clicks the shortcut, <First.exe> runs.
When <First.exe> terminates, <Second.exe> runs
When <Second.exe> terminates, <Third.exe> runs

An alternative method is to run a .BAT batch file under command.com (16 bit)

If Command Extensions are disabled, the START command will no longer recognise file Associations, and will not automatically evaluate the COMSPEC variable when starting a second CMD session.

Missing file extensions
When executing a command line whose first token does NOT contain an extension, then CMD.EXE uses the value of the PATHEXT environment variable to determine which extensions to look for and in what order. The default value for the PATHEXT variable is:

.COM;.EXE;.BAT;.CMD

Notice the syntax is the same as the PATH variable, with semicolons separating the different elements.

When executing a command, if there is no match on any extension, then NT will look to see if the name, without any extension, matches a directory name and if it does, the START command will launch Explorer on that path.

"Do not run; scorn running with thy heels" - Shakespeare, The Merchant of Venice

Related:

CALL - Call one batch program from another
CMD - can be used to call a subsequent batch and ALWAYS return even if errors occur.
Powershell: Invoke-Item - Invoke an executable or open a file (ii)
Q162059 - Opening Office documents
Equivalent bash command (Linux) : open - Open a file in its default application.