This work is an attempt to show that the known polytypes of silicon carbide can be considered to have their origins in screw dislocations. From theoretical considerations of dislocations in three phases of the compound, 6H, 4H, and 15 R, structural series (33 … 33), (33 … 34), (33 … 32), (22 … 22), (22 … 23) (22 … 21), (23 … 23), (23 … 33), and (23 … 22) are postulated. All polytypes reported in the literature are then outlined and their structures are compared with the theoretical predictions. The excellent correlation obtained, plus the fact that growth spirals exhibiting step heights of various magnitudes have been observed by many investigators of this compound, give much support to the idea that screw dislocations and the resulting spiral growth of the crystals produce these numerous structures.