The c(2\ifmmode\times\else\texttimes\fi{}2) reconstruction of the C-terminated 3C-SiC(001) surface has been characterized using first-principles density-functional calculations for a series of possible geometries. The bonding of the carbon atoms is found to be the key for understanding the surface reconstruction. The triple-bond bridging configuration is favored over the double-bond dimer reconstruction typical for group-IV (001) surfaces for reasons of energetic stability and the electronic structure. However, a partial dangling-bond saturation due to hydrogen cannot be excluded. Our results for the atomic and electronic structure agree reasonably with the experimental information available. \textcopyright{} 1996 The American Physical Society.