This third version of the DCAF-NATO PA ‘Vademecum’ underlines the essential role that parliaments must play in ensuring democratic oversight of the security sector. Updating key information on best practices related to parliamentary oversight and guidance of the security sector, the volume retains a special focus on defence affairs and puts the oversight role of parliament into political and military contexts. Aimed at democratic institutions within NATO partner-countries, it provides an introduction to the overarching principles of security sector reform and key oversight mechanisms and best practices.