As the global telecommunications industry moves into the next millennium, the difficulty, the frequency and the importance of interworking will increase due to three factors. First, as the last decade has shown, new technology is being created and deployed at an ever increasing rate and with higher complexity. This will result in greater difficulty to successfully interwork between technologies. Secondly, because competition has led to an increase in the number of carriers providing services, there will be more and more instances of interworking among carriers. Lastly, because all the carriers are hoping to be profitable, the interworking needs to be fast and easy to implement, have low costs and be seamless for users. Otherwise, increased costs and low customer satisfaction will reduce profits and possibly drive the carrier out of business. This paper will examine these assertions and discuss trends which support this proposition.