Change the user preference for the execution policy of the shell.

      Set-ExecutionPolicy [-executionPolicy] Policy
        { Unrestricted | RemoteSigned | AllSigned | Restricted | Default | Bypass | Undefined}
            [[-Scope] ExecutionPolicyScope ] [-Force]
               [-whatIf] [-confirm] [CommonParameters]

   -ExecutionPolicy Policy
       A new execution policy for the shell.

       Valid values:
       Do not load configuration files or run scripts.
       This is the default.
       Require that all scripts and configuration files be signed
       by a trusted publisher, including scripts that you write on the
       local computer.
       Require that all scripts and configuration files downloaded
       from the Internet be signed by a trusted publisher.
       Load all configuration files and run all scripts.
       If you run an unsigned script that was downloaded from the
       internet, you are prompted for permission before it runs.

       Nothing is blocked and there are no warnings or prompts.

       Remove the currently assigned execution policy from the
       current scope. This parameter will not remove an execution
       policy that is set in a Group Policy scope.

       Suppress all prompts.
       By default, Set-ExecutionPolicy displays a warning whenever the
       execution policy is changed.

    -Scope ExecutionPolicyScope
       The scope of the execution policy.

       Valid values:
         Process       Affect only the current PowerShell process.
         CurrentUser   Affect only the current user.
         LocalMachine  Affect all users of the computer.

       To remove an execution policy from a particular scope, set the
       execution policy for that scope to Undefined.

       Describe what would happen if you executed the command without actually
       executing the command.
       Prompt for confirmation before executing the command.

In order to change the Execution policy, you must be running PowerShell As Adminstrator.

ExecutionPolicy is like a baby door. The ExecutionPolicy keeps babies safe but every grown-up surpasses it easily. There are over 20 ways to surpass the ExecutionPolicy as a standard user. Therefore you should set it via GPO as you like it. (e.g. RemoteSigned)
It may prevent some people using PowerShell scripts from the internet but you should not count on it.

System-wide PowerShell Execution Policies have never been a way to prevent the user from doing something they want to do. That job is left to the Windows Account Model, which is a security boundary. [x]

Runing unsigned scripts

Even if the PowerShell execution policy is set to RemoteSigned it is still possible to run unsigned scripts:

Save the script file on your computer, Right-click the file, and click "Properties."
At the bottom of the dialogue box click "Unblock."

Alternatively copy the text into a brand new text file and save it with a .ps1 extension.

Bypass Execution policy completely

Microsoft never intended Execution policies to be a complete security control, so there are several ways to bypass them completely:

Pipe the contents of a script file to PowerShell.exe Std in:
Get-Content .demo.ps1 | PowerShell.exe -noprofile -

Or launch a one liner with invoke-command:
invoke-command -computername Server64 -scriptblock {Write-Host "demo"}

Several other methods can be found on the NetSPI blog here.

Change Execution policy once only...

To run a single PowerShell session with a different execution policy, use powershell.exe -ExecutionPolicy this will not affect the default policy setting for any future sessions.

64 bit vs 32 bit Execution policies

These will include both the 64bit and 32bit version of PowerShell, they each can have different execution policies, so you may wish to set both.
C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe = 64bit version
C:\Windows\SysWOW64\WindowsPowerShell\v1.0\powershell.exe = 32bit version


Set the user preference for the shell execution policy to RemoteSigned and then display the effective execution policy. The commands are separated by a semicolon (;)

PS C:\> set-executionpolicy remotesigned; get-executionPolicy

Get the execution policy from a remote computer, server64 and apply that execution policy to the local computer:

PS C:\> invoke-command -computername Server64 -scriptblock {get-executionpolicy} | set-executionpolicy -force

Set an execution policy of AllSigned for the current user, then the execution policies set in each scope:

PS C:\> set-executionpolicy -scope CurrentUser -executionPolicy AllSigned -force
PS C:\> get-executionpolicy -list

Set an execution policy value of Undefined to effectively remove the execution policy that is set for the current user scope. As a result, the execution policy that is set in Group Policy or in the LocalMachine (all users) scope is effective:

PS C:\> set-executionpolicy -scope CurrentUser -executionPolicy Undefined

If the execution policy in all scopes is set to Undefined and the Group Policy is not set, the default execution policy, Restricted, is effective for all users of the computer.

“Laughing on the way to your execution is not generally understood by less-advanced life forms, and they call you crazy” ~ Richard Bach

Related PowerShell Cmdlets

Set-AuthenticodeSignature - Sign a PowerShell script.
Get-ExecutionPolicy - Get the execution policy for the shell.

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