This article discusses the usefulness of niche overlap and niche overlap measures in studying competition. It is argued that (1) neither niche overlap nor niche overlap measures can be used to estimate the intensity of competition, but (2) niche overlap can be used to determine the relative amounts of inter— and intraspecific competition, while niche overlap measures are not useful in this regard. Before using overlap to estimate the relative intensities of inter— and intraspecific competition, it is necessary to have a model of the consumer—resource interaction, and some knowledge of the parameters in that model. The niche overlap and competition coefficient formulae proposed by Hurlbert (1978) are considered in some detail. Previously proposed niche overlap measures appear to be more useful than Hurlberts if one is interested in using the niche overlap measure for purely descriptive purposes.