Isotopic abundances in comets

Isotopic ratios in comets provide keys for the understanding of the origin of cometary material, and the physical and chemical conditions in the early Solar Nebula. We review here measurements acquired on the D/H, C-12/C-13, O-16/O-18, N-14/N-15, S-32/S-34 ratios in dust and gases, and discuss their cosmogonic implications. The prospects for future measurements from cometary space missions and remote sensing observations at millimeter and submillimeter wavelengths are presented.