Traditional single-mode fiber capacity issues will be mitigated by using space-division multiplexing in future 5G, IoT, and M2M networks. Multi-core fibers are expected as a good candidate for overcoming the capacity limit of a current optical communication system. This chapter describes the recent progress on the Multi-core fibers technology for the application of high capacity space-division multiplexing to be utilized for long-distance transmission systems. Further various optical approaches that enable key functions are discussed, including SDM MUX/DeMUX, switches, transceivers to enable next generation optical network. Moreover, issues like crosstalk, non-linearity is a potential limitation on the achievable data-rates in optical fiber transmission systems using multi-core fibers will be discussed.