The invasion of Iraq in 2003, and the Coalition Government's failure to win parliamentary approval for armed intervention in Syria in 2013, mark a period of increased scrutiny of the process by which the UK engages in armed conflict. For much of the media and civil society there now exists a constitutional convention which mandates that the Government consults Parliament before commencing hostilities. This is celebrated as representing a redistribution of power from the executive towards a more legitimate, democratic institution. This book offers a critical inquiry into Parliament's role in the war prerogative since the beginning of the twentieth century, evaluating whether the UK's decisions to engage in conflict meet the recognised standards of good governance: accountability, transparency and participation. The analysis reveals a number of persistent problems in the decision-making process, including Parliament's lack of access to relevant information, government 'legalisation' of parliamentary debates which frustrates broader discussions of political legitimacy, and the skewing of debates via the partial public disclosure of information based upon secret intelligence. The book offers solutions to these problems to reinvigorate parliamentary discourse and to address government withholding of classified information. It is essential reading for anyone interested in war powers, the relationship between international law and domestic politics, and the role of the Westminster Parliament in questions of national security.