New York mayor Mike Bloomberg seems to personify the interplay between business and politics in the US. He has clearly applied lessons learned in business to his approach to running the city.

The key lesson seems to be that if at first you don't succeed, seek a different route. At college, Bloomberg listed jobs he wanted: US president, UN secretary general and head of the World Bank. Instead, he built a business empire based on using technology to provide information for Wall Street.

Purnick's interesting account of Bloomberg's career asks how a "colourless manager" who "could not deliver a speech that anyone wanted to hear" became one of New York's most successful mayors.

A lifelong Democrat, he turned Republican to run for mayor, left the party as part of a bid to stand as an independent presidential candidate, before seeking its backing for a highly controversial third term.

This well balanced account focuses on Bloomberg's strengths and successes-a city-wide smoking ban, an environmental plan, good work on crime and education-as much as flaws and set backs.