Group Policy is Microsoft's centralized configuration management system for Windows domain environments. At its core, it's a hierarchical infrastructure that applies policy settings to computers and users in an Active Directory (AD) domain. These settings are stored in Group Policy Objects (GPOs) which get processed in a specific order:

1. Local GPOs (applied first)
2. Site-linked GPOs 
3. Domain-linked GPOs
4. OU-linked GPOs (applied last, taking precedence)

The Group Policy engine consists of several critical components:

• Client-Side Extensions (CSEs): DLLs that handle specific policy areas (e.g., Security CSE, Scripts CSE)
• Group Policy Container (GPC): AD object storing version information
• Group Policy Template (GPT): SYSVOL files containing actual policy settings

Here's how to create and link a GPO programmatically using PowerShell:

# Create new GPO
New-GPO -Name "Security Baseline" -Comment "Corporate security settings"

# Link GPO to OU
New-GPLink -Name "Security Baseline" -Target "OU=Workstations,DC=contoso,DC=com"

# Set registry policy (example)
Set-GPRegistryValue -Name "Security Baseline" -Key "HKLM\Software\Policies\Microsoft\WindowsFirewall" 
-ValueName "EnableFirewall" -Type DWORD -Value 1

Effective Group Policy administration involves:

• Implementing security baselines (e.g., CIS benchmarks)
• Managing software deployment through MSI packages
• Controlling user environment with folder redirection
• Enforcing password and account lockout policies

Essential commands for diagnostics:

# Force policy update on client
gpupdate /force

# Check applied policies
gpresult /h report.html

# Check policy processing details
Get-GPResultantSetOfPolicy -ReportType Html -Path "C:\report.html"

Important differences across Windows versions:

Group Policy Objects (GPOs) form the backbone of enterprise Windows administration, enabling centralized management of computer and user configurations across Active Directory (AD) domains. At its core, GPO delivers hierarchical policy enforcement through these key components:

// Sample GPO structure representation
AD Domain
├── Site-level GPOs
│   └── (Applies to all domain-joined machines in physical location)
├── Domain-level GPOs
│   └── (Default Domain Policy, security baselines)
└── Organizational Unit (OU) GPOs
    ├── Workstations OU
    │   └── (Drive mappings, power settings)
    └── Servers OU
        ├── Member Servers
        │   └── (Windows Update policies)
        └── Domain Controllers
            └── (Password policies, auditing)

The processing order follows the LSDOU rule (Local, Site, Domain, Organizational Unit) with these critical aspects:

• Client-Side Extensions (CSEs): Handle specific policy areas like Registry preferences (Registry CSE) or security settings (Security CSE)
• WMI Filtering: Allows conditional application based on system properties
• Loopback Processing: Merges or replaces user policies when logging onto specific machines

Modern administration heavily utilizes PowerShell for GPO operations. Here are essential cmdlets:

# Create and link new GPO
New-GPO -Name "Workstation Baseline" | 
New-GPLink -Target "OU=Workstations,DC=domain,DC=com"

# Backup all GPOs
Backup-GPO -All -Path "\\fileserver\gpo_backups"

# Apply security filtering
Get-GPO -Name "Sales Team Policies" | 
Set-GPPermission -TargetName "Sales_Group" -TargetType Group -PermissionLevel GpoApply

# Diagnostic commands
Get-GPOReport -Name "Default Domain Policy" -ReportType Html -Path "C:\temp\report.html"
Get-GPResultantSetOfPolicy -Computer "ClientPC01" -User "Domain\User" -ReportType Html

When policies fail to apply, check these areas:

1. Run gpresult /h report.html on affected machine
2. Verify DNS resolution and DC availability
3. Check Event Viewer's Application log for CSE errors
4. Test with gpupdate /force and review resultant set

For complex environments, consider: