A theft amounting to £1 was a capital offence in 1260 and a judge in 1610 affirmed the law could not then be applied since £1 was no longer what it was. Such association of money with a date is well recognized for its importance in very many different connections. Thus arises the need to know how to convert an amount at one date into an equivalent amount at another date. In other words, a price index. The ordinary consumer price index or CPI represents a practical response to the need. A sense for the equivalence that should give it some legitimacy, and the faithfulness or truth of a price index to that sense, becomes an issue giving rise to extensive thought and theory about price indices, to which over the decades a remarkable number of economists have each contributed a word, or volume. However, there have been hold-ups at a most basic level, cleared in this book. Beside the classical part of the subject that should command most attention, this volume ventures into further topics. Afriat is rightly famous for his work in the field of the price index and this latest book will interest economists of an academic and professional nature the world over.