The international community uses a number of interventions to make and build peace. How effective are these interventions? What works and what does not? The discussion highlights the uncertainties when evaluating interventions. Although some interventions are frequently advocated we know very little about their success. Some of the commonly advocated interventions have been assessed in large n-studies. Although there is no evidence that development aid helps to prevent wars, there is evidence that aid stabilizes post-war situations. There are also a number of studies suggesting that UN Peace Keeping Operations do indeed keep the peace. Although there are fewer studies, there is some emerging evidence that arms embargoes do restrict arms transfers to conflict zones and thus help to make conflicts less deadly. The discussion also suggests that internationally binding rules on arms transfers and the use of private military and security services would support conflict prevention.