Relativity: The Special and the General Theory is a popular science book by Albert Einstein. It began as a short paper and was eventually expanded into a book written with the aim of explaining the special and general theories of relativity. It was published in German in 1916 and translated into English in 1920. It is divided into three parts, the first dealing with special relativity, the second dealing with general relativity, and the third dealing with cosmology. (Wikipedia, CC BY-SA 4.0)