The move from territorial defence to ‘wars of choice’ has influenced the domestic politics of military interventions. This paper examines the extent to which both the substance and the procedure of military interventions are contested among political parties. Regarding the substance, our analysis of Chapel Hill Expert Survey data demonstrates that across European states political parties on the right are more supportive of military missions than those on the left. On the decision-making procedures, our case studies of Germany, France, Spain and the United Kingdom show that political parties on the left tend to favour strong parliamentary control whereas those on the right tend to prefer an unconstrained executive, although with differences across countries. These findings challenge the view that ‘politics stops at the water's edge’ and contribute to a better understanding of how political parties and parliaments influence military interventions.