Publisher Summary Hoxa-13 is expressed along a posterior embryo body axis and in developing limbs. At early stages of development, Hoxa-13 expression is restricted to a domain towards the posterior and distal region of the limb buds. At later stages, Hoxa-13 is expressed in the whole autopod region. This chapter presents a study in which mutation of Hoxa-13 showed a semidominant phenotype. Heterozygous mutants were viable and displayed partial syndactyly in the forelimbs. Homozygous disruption resulted in lethality between E11.5 and E14.5 and specific alterations of the developing skeleton in the limb autopod. The first digit cartilage condensations were missing and some carpal and tarsal cartilages were absent. The results of this study suggest that synergistic effects of Hoxa-13 and Hoxd-13 mutations occur in the early patterning of the limb autopod.