RUNAS

Execute a program under a different user account.

Syntax
      RUNAS [/profile] [/env] [/netonly] /user:user Program

Key
   /profile   Option to load the user's profile (registry)
   /env       Use current environment instead of user's.
   /netonly   Use the credentials specified only for remote connections.
   /user      Username in form USER@DOMAIN or DOMAIN\USER
              (USER@DOMAIN is not compatible with /netonly)
   Program    The command to execute

Enter the password when prompted.

When you start a program with RunAs /netonly, the program will execute on your local computer as the user you are currently logged on as, but any connections to other computers on the network will be made using the user account specified.

Without /netonly everything will run under the user account specified.

RunAs from Windows Explorer
Select an executable file, Shift-Right-click and select Run As..
This option can be hidden by setting
HKLM\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer
HideRunAsVerb=1

ErrorLevel
The error level (%ERRORLEVEL%) returned by RunAs in Windows XP and above: success=0, failure=1

Run with Elevated permissions

In Windows Vista and above, you can run a script with elevated permissions by right clicking and choosing "Run As Administrator" but it’s also possible to invoke the UAC dialogue by calling the VBScript .ShellExecute function.

When a script is run with elevated permissions several aspects of the user environment may change: The current directory, the current TEMP folder and any mapped drives will be disconnected.

Examples

Run mycommand.exe as the user Jdoe on domain SS64dom

   Runas /user:SS64Dom\jDoe "mycommand.exe"

Run CMD.exe as the Administrator on the local machine:

   Runas /profile /user:DELLPC218\administrator CMD

Run Notepad.exe as the Domain Administrator on domain SS64dom

   Runas /profile /env /user:SS64Dom\administrator NOTEPAD

Run Notepad.exe and open a file, escape the quote characters around the filename with \

   Runas /env /user:jDoe@swest.ss64.com "NOTEPAD \"my file.txt\""

Notes:
The backslash \ is NOT the standard escape character used by other CMD commands.
RunAs Reqires the "Secondary Logon" service to be running.

“He who reigns within himself, and rules passions, desires, and fears, is more than a king” ~ Milton

Related:

ShellRunAs - Run a command under a different user account
Aaron Margosis - Running with least privilege
joeware.net - CPAU (Create Process As User) like RunAs but with an options to encrypt the password.
PsExec - Execute process remotely
Powershell: you can run an entire powershell session via RunAs to elevate your permissions.
Equivalent bash command (Linux): SU - Switch User