PowerShell Constrained Language Mode is a security feature in Microsoft PowerShell that restricts the language elements and cmdlets available for use. When enabled, it limits scripts and commands to a safe subset of functionality, reducing the risk of malicious code execution. This mode is often activated automatically in environments with application whitelisting or Device Guard policies. It blocks advanced features such as .NET type usage, custom classes, and certain cmdlets, making it harder for attackers to exploit PowerShell for lateral movement or privilege escalation. Constrained Language Mode is a key defense mechanism in securing Windows environments against script-based attacks.