In the age of Web 2.0 the internet as a platform to provide services or sell goods gained more attention in companies. Especially for customer support customer forums can be a useful tool for companies. By providing customer forums, companies can reduce their support costs dramatically. Nevertheless, it is often difficult for companies to measure the success of customer forums. In the research literature the determinants of success of customer forums have seldom been studied. The purpose of this bachelor thesis is to fill this research gap by applying the model of Lin and Lee to measure the success of online-communities on customer forums. In addition, metrics for measuring the success of this model are discussed. The discussion of this topic leads to the conclusion that the model of Lin and Lee is mostly applicable for customer forums, and provides a useful approach to measuring suc-cess both in theory and in practice. This could be demonstrated by the example of the 1&1 customer forum. The metrics that were found in the theoretical part were quite relevant in practice. Nevertheless, future research should focus more on monetary indicators to also make success of customer forums financially assessable.