Expression of the β3 subunit of the αvβ3 vitronectin receptor on melanoma cells is associated with tumor thickness and the ability to invade and metastasize. To address the role of αvβ3 in the complex process of progression from the nontumorigenic radial to the tumorigenic vertical growth phase of primary melanoma, we examined the biological consequences of overexpressing αvβ3 in early-stage melanoma cells using an adenoviral vector for gene transfer. Overexpression of functional αvβ3 in radial growth phase primary melanoma cells 1) promotes both anchorage-dependent and -independent growth, 2) initiates invasive growth from the epidermis into the dermis in three-dimensional skin reconstructs, 3) prevents apoptosis of invading cells, and 4) increases tumor growth in vivo. Thus, αvβ3 serves diverse biological functions during the progression from the nontumorigenic radial growth phase to the tumorigenic and invasive vertical growth phase primary melanoma.