"How does a photon get into an atom?" This question - fundamental to quantum mechanics - puzzled leading scientists such as Schrödinger and Heisenberg and is still asked by students. James D. Macomber's book was the first to provide a didactic and unified approach to the answer, which has now been updated by way of recent experimental results and modern theoretical interpretations written by leading scientists. It provides an understanding for similarities among the spectroscopic methods available and is stimulating to read, reflecting the excitement of scientific research.