This paper summarizes the contributions to Group 15 of Genetic Analysis Workshop (GAW) 14, which focused on methods for dealing with heterogeneity in linkage and association analysis. A variety of methods were employed, ranging from manipulation of the phenotype and/or identification of endophenotypes prior to analysis, to statistical methods allowing for heterogeneity in the analysis of simple dichotomous phenotypes as provided with the data. Overall, it was difficult to draw broad conclusions from these applications. Groups that focused on the simulated data had fairly consistent success in mapping the major genes (but not the two minor genes). However, this appeared to be the case regardless of whether heterogeneity was explicitly modeled, either at the phenotypic or statistical level, with relatively crude statistical methods applied to the simulated simple dichotomous trait Kofendrerd personality disorder also enjoying considerable success. Genet. Epidemiol. 29(Suppl. 1):S110–S115, 2005. © 2005 Wiley-Liss, Inc.