This is a collection of papers by leading theorist Robert A Pollak - four of them previously unpublished - exploring the theory of the cost of living index. The unifying theme of these papers is that, when suitably elaborated, the theory of the cost of living index provides principled answers to many of the practical problems that arise in constructing consumer price indexes.In addition to Pollak's classic paper The Theory of the Cost of Living Index, the volume includes papers on subindexes, the intertemporal cost of living index, welfare comparisons and equivalence scales, the social cost of living index, the treatment of `quality', and consumer durables in the cost of living index.