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 if the credentials specified are for RAS only.
   /user      Username in form USER@DOMAIN or DOMAIN\USER
              (USER@DOMAIN is not compatible with /netonly)
   Program    The command to execute

Examples:
   runas /profile /user:mymachine\administrator CMD
   runas /profile /env /user:SCOT_DOMAIN\administrator NOTEPAD
   runas /env /user:jDoe@swest.ss64.com "NOTEPAD \"my file.txt\""

Enter the password when prompted.

RunAs from the Windows explorer GUI
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 is not consistent between operating systems
In Windows 2000: success=1, failure=0
In Windows XP and above: success=0, failure=1

Example

 RUNAS /user:SCOT_DOMAIN\jDoe"mycommand.exe"

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:

AT - Run a command on a remote machine (at a scheduled time)
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