In the last 20 years, Geographic Information Systems (GISs) have had an ever-increasing impact on the course of research and planning in many diverse fields, including geography, geology, environmental studies, business and criminal justice. Relatively recently, health care research, including cancer research, has entered this domain. The rapidly increasing use of GIS in health-care research over the past few years is witnessed by the fact that 63% of papers in literature review for this chapter were written in the last five years, and 35% within the last three years. Epidemiology, the study of disease patterns in human populations according to person, place and time, has been the traditional means of approaching cancer etiology. Combining its tools with those of GIS has enabled researchers to look at the distribution of cancer in new ways and uncover relationships not previously seen with traditional epidemiological methods alone. Through its data integration function, GIS has enabled the use of existing data collected for other purposes to be applied to cancer research. GIS techniques can enhance the visualization of spatial patterns of cancer, examine the contribution of various risk factors for cancer in new ways and allow hypotheses about cancer etiology to be tested in a spatial framework. The purpose of this chapter is to examine the impact of GIS on the direction of cancer research. In doing so, it will consider the application of GIS techniques to research in cancer etiology and compare them to traditional epidemiological methods. Rather than an exhaustive compilation of all the studies in this category, selective examples will be chosen from the literature to illustrate particular applications.