The structures of free-standing gold nanowires are studied by using molecular-dynamics-based genetic algorithm simulations. Helical and multiwalled cylindrical structures are found for the thinner nanowires, while bulk-like fcc structures eventually form in the thicker nanowires up to 3 nm in diameter. This noncrystalline-crystalline transition starts from the core region of nanowires. The vibrational, electronic, and transport properties of nanowires are investigated based on the optimal structures. Bulklike behaviors are found for the vibrational and electronic properties of the nanowires with fcc crystalline structure. The conductance of nanowires generally increases with wire diameter and depends on the wire structure.