A primary challenge in biomedical research today is the elucidation of the underlying genetic architecture of complex conditions such as obesity. In contrast to simple Mendelian disorders that result from a mutation in a single gene, complex phenotypes are the product of the action (as well as interaction) of multiple genes and environmental factors. The genetic configuration of these genes can range from effectively polygenic (i.e., many genes each with a relatively small contribution) to oligogenic (i.e., a few genes with relatively large measurable effects often expressed on a residual additive genetic background). While the task at hand is complicated, it is not intractable; however, it does require consideration of the nature of the disease and definition of its associated phenotypes in selecting the most appropriate study design. Here we will discuss the characteristics of obesity and its related phenotypes, which must be considered in designing analyses to identify the genes involved as well as reviewing what these approaches have provided in the search for genes influencing adiposity in humans