This is the first ever compendium of double photoionisation spectra, covering some 70 of the most important small and medium sized molecules and thus providing an essential starting point for studies of the consequences of ionisation by high energy photons in both terrestrial and astrophysical environments. It also provides a complete non-mathematical description of all the phenomena and pathways involved in molecular double photoionisation. Most spectra are presented with identification of the electronic states and leading orbital configurations. The technique of magnetic bottle time-of-flight electron spectroscopy, used for all the spectra, is fully explained and compared with other techniques. For each molecule, the book gives full references to relevant work by complementary techniques and to theoretical calculations. Written in a clear non-mathematical style, this book is accessible to students as well as more experienced researchers. The authors have designed the layout for easy retrieval of any desired spectrum through the systematic organisation and ordering of the compounds and thorough indexing. As well as being a compendium of spectra, the book is a textbook covering all the known phenomenological aspects of molecular double photoionisation. The important phenomena are first mentioned in the introductory chapters, and are discussed in more detail in connection with the groups of molecules and individual cases where they are most relevant. The most useful spectra will be available in digital form for users.