AbstractHome range patterns of squirrels in the generaSciurusandTamiasciurusare reviewed. Emphasis is placed on the need to use analytical techniques which are appropriate to the questions of interest, and certain weaknesses in published studies are outlined. Variation in home range size between different species, populations of the same species and individuals of the same population is discussed in relation to ecological theory and the biology of tree squirrels. Larger species do not necessarily have larger home ranges. There is an inverse relationship between home range size and population density, but its interpretation is not clear in the absence of experimental studies. Differential utilization of space within the home range is considered to be a common pattern, although it is rarely explicitly described in tree squirrel studies. In general, species of the genusTamiasciurusdefend exclusive territories, whilst those of the genusSciurusdo not. Explanations for these patterns are discussed in terms of ‘economic defendability’ and resource heterogeneity. Problems for future study are sugges