From the reviews:

"Here is another book which is centered around the SO(4)-invariance of the 1/r potential. … the present author always remains on a very solid mathematical ground. … The author prepares carefully the mathematical ingredients (Hilbert spaces, Lie groups, Lie algebras, representations). The style of this senior-level undergraduate text is very fluent and – in the best sense – entertaining." (Evelyn Weimar-Woods, Zentralblatt MATH, Vol. 1088 (14), 2006)

"It is an introductory textbook on the unitary representation theory of Lie groups, with emphasis on the important groups SO (3), SU (2), and SO (4), with the hydrogen atom as a motivating, unifying theme. The intended audience is senior-level undergraduate majors in mathematics, physics, and chemistry. Numerous exercises are provided. … will recommend the book as supplementary reading to those students who desire to understand the mathematics at a deeper level. … Singer’s book is a very good one for undergraduate mathematics majors." (Stephen A. Fulling, American Mathematical Monthly, Vol. 114, August-September, 2007)