Activation and deactivation hooks manage plugin lifecycle events. Use register_activation_hook to execute setup code when plugins activate. Common tasks include creating database tables, setting default options, and scheduling cron jobs. The register_deactivation_hook cleans up temporary data and unschedules events. Never deactivate other plugins programmatically. Avoid complex operations during activation to prevent timeouts. Use uninstall.php or register_uninstall_hook for complete removal. Test activation on different WordPress versions and configurations. Proper lifecycle management ensures smooth plugin installation and removal experiences.