"The book is written in a very concise, clear, and elegant way. Misprints are rare... There are no exercises, but the book is well equipped with examples, which help to understand the assertions and are, as a rule, of independent interest. To sum up, the text presents an extremely interesting account of some of the most important developments in the chosen direction." -MATHEMATICAL REVIEWS "The boal of the book under review is to present a method for examing the surprising connection between invariant differential operators and almost periodic operators on Lie groups with polynomial growth... The book is deveoted to a very interesting topic. It is aimed to graduate studetns as well as researchers, and it can be highly recommended." ---ZAA