Group Policy is a feature of the Microsoft Windows NT family of operating systems that control the working environment of user accounts and computer accounts. Group Policy provides the centralized management and configuration of operating systems, applications, and users' settings in an Active Directory environment.
Group Policy in part controls what users can and cannot do on a computer system, for example: to enforce a password complexity policy that prevents users from choosing an overly simple password, to allow or prevent unidentified users from remote computers to connect to a network share, to block access to the Windows Task Manager or to restrict access to certain folders. A set of such configurations is called a Group Policy Object (GPO).
As part of Microsoft's IntelliMirror technologies, Group Policy aims to reduce the cost of supporting users. IntelliMirror technologies relate to the management of disconnected machines or roaming users and include roaming user profiles, folder redirection, and offline files.
To accomplish the goal of central management of a group of computers, machines should receive and enforce GPOs. A GPO that resides on a single machine only applies to that computer. To apply a GPO to a group of computers, Group Policy relies on Active Directory (or third party products like ZENworks Desktop Management) for distribution. Active Directory can distribute GPOs to computers that are part of a Windows domain.
By default, Microsoft Windows refreshes its policy settings every 90 minutes with a random 30 minutes offset. On Domain controllers, Microsoft Windows does so every five minutes. During the refresh, it discovers, fetches and applies all GPOs that apply to the machine and logged on user. Some settings, such as automated software installation, drive mappings, startup scripts or logon scripts are only applied during startup or user logon. Since Windows XP, a refresh of the group policy can be manually initiated by the user using the
gpupdate command from a command prompt.
Group Policy Objects are processed in the following order (from top to bottom):
- Local - Any settings in the computer's local policy. Prior to Windows Vista, there was only one local group policy stored per computer. Windows Vista and later Windows versions allow individual group policies per user accounts.
- Site - Any Group Policies associated with the Active Directory site in which the computer resides. (An Active Directory site is a logical grouping of computers that is meant to facilitate management of computers based on their physical proximity.) If multiple policies are linked to a site, they are processed in the order set by the administrator.
- Domain - Any Group Policies associated with the Windows domain in which the computer resides. If multiple policies are linked to a domain, they are processed in the order set by the administrator.
- Organizational Unit - Group policies assigned to the Active Directory organizational unit (OU) in which the computer or user are placed. (OUs are logical units that help organizing and managing a group of users, computers or other Active Directory objects.) If multiple policies are linked to an OU, they are processed in the order set by the administrator.
A policy setting inside a hierarchical structure is ordinarily passed from parent to children, and from children to grandchildren, and so forth. This is termed inheritance. It can be blocked or enforced to control what policies are applied at each level. If a higher level administrator (enterprise administrator) creates a policy that has inheritance blocked by a lower level administrator (domain administrator), this policy will still be processed.
Where a Group Policy Preference Settings is configured and there is also an equivalent Group Policy Setting configured, then the value of the Group Policy Setting will take precedence.
WMI filtering is the process of customizing the scope of the GPO by choosing a Windows Management Instrumentation (WMI) filter to apply. These filters allow administrators to apply the GPO only to, for example, computers of specific models, ram amounts, installed software, anything available via WMI queries.
Local Group Policy 
Local Group Policy (LGP) is a more basic version of the Group Policy used by Active Directory. Prior to Windows Vista, LGP could enforce a GPO for a single local computer, but could not make policies for individual users or groups. Windows Vista allows setting local Group Policy for individual users. LGP can be applied to a computer on a domain, and it can be used on Windows XP Home Edition.
Group Policy preferences 
There is a set of group policy setting extensions that were previously known as PolicyMaker. Microsoft bought PolicyMaker and then integrated them with Windows Server 2008. Microsoft has since released a migration tool that allows users to migrate PolicyMaker items to Group Policy Preferences.
Group Policy Preferences adds a number of new configuration items. These items also have a number of additional targeting options that can be used to granularly control the application of these setting items.
Group Policy Preferences are compatible with x86 and x64 versions of Windows XP, Windows Server 2003, and Windows Vista with the addition of the Client Side Extensions (also known as CSE).
Group Policy Management Console 
Originally, Group Polices were modified using the Group Policy Edit tool that was integrated with Active Directory Users and Computers Microsoft Management Console (MMC) snap-in, but it was later split into a separate MMC snap-in called the Group Policy Management Console (GPMC). The GPMC is now a user component in Windows Server 2008 and Windows Server 2008 R2 and is provided as a download as part of the Remote Server Administration Tools for Windows Vista and Windows 7.
Advanced Group Policy Management 
Microsoft has also released a tool to make changes to Group Policy called Advanced Group Policy Management (a.k.a. AGPM). This tool available for any organization that has licensed the Microsoft Desktop Optimization Pack (a.k.a. MDOP). This advanced tool allows administrators to have a check in/out process for modification Group Policy Objects, track changes to Group Policy Objects, and implement approval workflows for changes to Group Policy Objects.
AGPM consists of two parts - server and client. The server is a Windows Service that stores its Group Policy Objects in an archive located on the same computer or a network share. The client is a snap-in to the Group Policy Management Console, and connects to the AGPM server. Configuration of the client is performed via Group Policy.
Group Policy settings are enforced voluntarily by the targeted applications. In many cases, this merely consists of disabling the user interface for a particular function without disabling lower-level means of accessing it.
Alternatively, a malevolent user can modify or interfere with the application so that it cannot successfully read its Group Policy settings, thus enforcing potentially lower security defaults or even returning arbitrary values.
Windows 8 enhancements 
Windows 8 introduced a new feature called Group Policy Update. This feature allows an administrator to force a group policy update on all computers with accounts in a particular Organizational Unit. This update creates a scheduled task on the computer and it will run the GPUPDATE command within 10 minutes with a random offset to not over load the domain controller.
Group Policy Infrastructure Status which can report when any Group Policy Objects are not replicated correct amongst domain controllers.
Group Policy Results Report also has a new feature that times the execution of individual components when doing a Group Policy Update.
See also 
- "Group Policy processing and precedence". Microsoft Corporation. 22 April 2012.
- Group Policy - Apply to a Specific User or Group - Windows 7 Forums
- Step-by-Step Guide to Managing Multiple Local Group Policy Objects
- Group Policy Preference Migration Tool (GPPMIG)
- Group Policy Preference Client Side Extensions for Windows XP (KB943729)
- Group Policy Preference Client Side Extensions for Windows XP x64 Edition (KB943729)
- Group Policy Preference Client Side Extensions for Windows Vista (KB943729)
- Group Policy Preference Client Side Extensions for Windows Vista x64 Edition (KB943729)
- Group Policy Preference Client Side Extensions for Windows Server 2003 (KB943729)
- Group Policy Preference Client Side Extensions for Windows Server 2003 x64 Edition (KB943729)
- Microsoft Group Policy Team (2009-12-23). "How to Install GPMC on Server 2008, 2008 R2, and Windows 7 (via RSAT)".
- Microsoft Remote Server Administration Tools for Windows Vista
- Microsoft Remote Server Administration Tools for Windows Vista for x64-based Systems
- Remote Server Administration Tools for Windows 7
- Microsoft Windows Enterprise | Enhancing Group Policy
- Raymond Chen, "Shell policy is not the same as security"
- Mark Russinovich, "Circumventing Group Policy as a Limited User
- Updated: What’s new with Group Policy in Windows 8
- Windows 8 Group Policy Performance Troubleshooting Feature
Further reading 
- "Group Policy for Beginners". Windows 7 Technical Library. Microsoft. 27 April 2011. Retrieved 22 April 2012.
- "Group Policy Management Console". Dev Center - Desktop. Microsoft. 3 February 2012. Retrieved 22 April 2012.
- "Step-by-Step Guide to Managing Multiple Local Group Policy Objects". Windows Vista Technical Library. Microsoft. Retrieved 22 April 2012.
- "Group Policy processing and precedence". Windows Server 2003 Product Help. Microsoft. 21 January 2005. Retrieved 22 April 2012.
- Official website
- Group Policy Team Blog
- Group Policy Settings Reference for Windows and Windows Server