Huntington’s disease (HD) research is aimed at understanding the root cause of the disorder, for the thrill of uncovering new biology, and for the serious purpose of finding effective therapeutic agents. Molecular genetics has revealed the disease trigger, an inherited unstable CAG expansion in a novel 4p16.3 gene (HD), that lengthens a polyglutamine segment in huntingtin. Now studies with HD patients and model systems that are genetic HD replicas are homing in on the trigger mechanism and the first formative steps that cast HD as a distinct clinical entity. At the same time, assays at the biochemical, cellular, and whole organism levels are starting to yield potential disease modifying genes and candidate drugs. These can be prioritized by testing in a panel of genetic and phenotypic HD mouse models to yield analytical tools for dissecting the early and late stages of the disease process and to maximize the chance of success in trials with HD patients.