Open Source Software (OSS) has reached widespread popularity within the last years not least because of renowned products such as Linux, the Apache Web Server or the Mozilla project. Under the Open Source Software Development (OSSD) model products are launched in rapid succession and with high quality, without following traditional quality practices of accepted software development models [1]. Furthermore, some OSSD projects challenge established Quality Assurance (QA) approaches, claiming to be successful through partially contrary techniques. The aim of this research is to improve the understanding of QA practices under the OSSD model. A survey research method is used to gain empirical evidence about applied QA practices in mid-size to large OSS projects. A further evaluation of successful projects results that they apply well-structured and organized development processes. The findings provide evidence for Raymond's lifecycle and show that OSS projects leverage their communities effectively.