SNPs are highly abundant in the human genome, explaining most of sequence variation. This makes them a valuable resource for population genetics, evolution, and gene mapping. In this article we have given an overview of the major issues arising in their application to haplotype and haplotype block estimation and genetic association. The discussion should make clear that many statistical methods have been developed for these problems, but there is still much more to understand about the relative merits of the competing methods. Perhaps more important is further understanding of the practical utility of the methods.