Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. PyMOL is an open-source, user-sponsored, molecular visualization system created by Warren Lyford DeLano and commercialized by DeLano Scientific LLC, which is a private software company dedicated to creating useful tools that become universally accessible to scientific and educational communities. It is well suited to producing high quality 3D images of small molecules and biological macromolecules such as proteins. According to the author, almost a quarter of all published images of 3D protein structures in the scientific literature were made using PyMOL. PyMOL is one of few open source visualization tools available for use in structural biology. The Py portion of the software's name refers to the fact that it extends, and is extensible by the Python programming language.