How can I get the file system location of a PowerShell script?

PowerShell 3+

The path of a running scripts is:

$PSCommandPath

Its directory is:

$PSScriptRoot

PowerShell 2

The path of a running scripts is:

$MyInvocation.MyCommand.Path

Its directory is:

$PSScriptRoot = Split-Path $MyInvocation.MyCommand.Path -Parent

Roman Kuzmin answered the question imho. I'll just add that if you import a module (via Import-Module), you can access $PsScriptRoot automatic variable inside the module -- that will tell you where the module is located.