Nature seldom draws a straight line. This is more apparent in the anatomy of the teeth roots and root canal system of human teeth. The root with a graceful, tapering canal and a single apical foramen is the exception than the rule. Even teeth with straight roots can harbor severely curved canals. In fact, curved canals are the most common endodontic complexity.The root canal anatomy of each tooth has certain common characteristics as well as numerous atypical ones that can be road maps to successful endodontics.