von Willebrand disease (VWD) is a clinically heterogeneous bleeding disorder that reflects a wide array of defects. Quantitative subtypes of the disorder, including types 1 and 3 VWD, result in bleeding due to reduced levels of circulating von Willebrand factor (VWF) protein. Qualitative subtypes, defined as type 2 VWD, act through altered VWF function. A range of molecular defects are responsible for many of these subtypes, including missense, nonsense, splicing, insertion, and deletion mutations, resulting in either dominant or recessive inheritance. While many mutations correspond to selected variants, the basis for variation in expression and the imperfect correlations between genotype and phenotype remain to be understood.