Conditions influencing the distribution and abundance of Ixodes scapularis Say in North America have been the object of considerable study during the past 2 decades, resulting in new information about its expanding range, population structure, host associations, and environmental constraints. Variation in the methods, timing, or extent of sampling, the type of population estimate developed, and the spatial scale of analysis makes comparisons of results difficult. This report summarizes research on I. scapularis habitat, including the diversity of hosts and physical conditions in the environment where they are abundant, and how this may influence dispersal and range expansion. Recent efforts to analytically address spatial distributions are considered. Approaches that may be useful in clarifying and resolving unanswered questions are suggested, and a conceptual framework for analyzing this vector's expanding abundance and distribution is offered.