BPMN is a standard for modeling business processes and provides meta model concepts for the design of extensions. Thus, domain-specific extensions of the BPMN are facilitated. This research article provides an overview of BPMN extension development by the descriptive analysis and classification of 30 BPMN extensions. An extensive literature review was conducted in order to find published extensions. Further, a classification framework was designed to enable a comprehensive analysis of each extension. The analysis showed, that four out of five extensions are not compliant with the BPMN standard. Also, we found several methodological shortcomings that should be tackled in further research.