Genetics and biochemistry are great tools and provide a lot of information, but these approaches are insufficient to understand how one protein can function in different molecular contexts or molecular machines. The isolation and analysis of the molecular machines offers the possibility to study a protein of interest in the context of its function and partners carrying out specific functions. Applications of this technology will help to understand all kinds of multi-step processing pathways, including stable machinery of the metabolism or cell cycle, but also transient interactions in signal transduction and trafficking.