Schizophrenia and bipolar illness are two of the most serious forms of mental illness. Until relatively recently, almost nothing was known about the molecular pathogenesis of either illness. The single largest risk factor that predisposes people to schizophrenia or bipolar illness is genetic risk. Heritability is high, and the incidence is significantly higher in identical twins than in nonidentical twins. Despite decades of work aimed at identifying the genes involved in these two illnesses, virtually no progress had beenmade until the past decade. With the knowledge and technologies that have been gained from theHumanGenome Project, ithas been possible to begin to understand the underlying genetics and to use the new information to begin the effort to discover new and better medicines to treat these illnesses. This articlewilldescribe the past decade of work toward this goal and articulate both the promise thatnowexists andwhat is still neededto bringdramatic andtangible change topatients-Scolnick, E. M. Thepath to new therapies for schizophrenia and bipolar illness.