The Golden Ratio : The Story of PHI, the World's Most Astonishing Number by Mario Livio is a book about a number. the number phi (Φ). Φ is an irrational number like pi (π). Φ is equal to 1.618033988749895... The number Φ is intimately related to the Fibonacci series [0,1,1,2,3,5,8,13,21,34...] and it pops up in a surprising number of places. in fact a bit of a numerological cult has developed around it.

The Livio book is all about Φ and its history. Livio points out where Φ is found in nature and geometry and art. Livio also plays myth-buster and debunks those claims by golden ratio mystics who find Φ where it is not.

This book is a tough read for a layman but armchair mathematicians will find it fascinating.