Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is a heritable disorder characterized by right ventricular enlargement and dysfunction, fibrofatty replacement of cardiomyocytes, and arrhythmias. Presenting symptoms include palpitations, syncope, heart failure, or sudden cardiac death. The disease has an incidence of one in 5000 and typically displays autosomal dominant inheritance with incomplete penetrance and variable expressivity. We sought to further characterize the genetic basis for this life-threatening cardiomyopathy and identify novel disease-causing genes in ARVD/C. We describe the first recessive mutation in the plakophilin-2 gene (PKP2), and show that it creates a cryptic splice site resulting in a translational frame shift. We also find that heterozygous mutations in the desmosomal gene desmoglein-2 (DSG2) cause ARVD/C in a subset of familial cases. These findings not only implicate the cardiac desmosome as the key pathogenetic structure mutated in ARVD/C but also aid in the diagnosis of suspected probands and in the screening of family members. In addition to these recent genetic advances, this thesis will also focus on current hypotheses on disease mechanism as well as the role of clinical genetic testing in diagnosis and prognosis of ARVD/C.