This is an invaluable book for all those who use (or interpret the output of) POLIMOD, Cambridge University’s Microsimulation Unit’s tax and benefit model. The book provides an illustration of the type of analysis an arithmetic model like POLIMOD can perform, and demonstrates the sensitivity of results to some of the key assumptions that can be made in carrying out a microsimulation analysis. It covers the model’s construction, modelling assumptions and the model outputs. The study also offers those directly involved in the development of microsimulation models a guide to the types of data and modelling problems often encountered, as well as a record of one specific approach to dealing with them. Published by Cambridge University Press, 1998, ISBN 0 521 63224 2 (hardback), price £35.00 (US$59.95).