The paper provides a comprehensive overview of Non-Orthogonal Multiple Access (NOMA) technology, which is crucial for addressing the challenges of supporting large-scale heterogeneous data traffic in 5G networks. NOMA, introduced for 3GPP-LTE-A, allows multiple users to share the same orthogonal resource block, enhancing bandwidth efficiency compared to conventional Orthogonal Multiple Access (OMA). The authors highlight the theoretical principles of NOMA, multiple antenna-aided NOMA design, cooperative transmission, resource control, and the integration of NOMA with other 5G techniques. They also discuss the advantages of power-domain multiplexing NOMA over other NOMA techniques and identify key research challenges and potential solutions. The paper concludes with design guidelines for NOMA systems and identifies promising research opportunities for future advancements.The paper provides a comprehensive overview of Non-Orthogonal Multiple Access (NOMA) technology, which is crucial for addressing the challenges of supporting large-scale heterogeneous data traffic in 5G networks. NOMA, introduced for 3GPP-LTE-A, allows multiple users to share the same orthogonal resource block, enhancing bandwidth efficiency compared to conventional Orthogonal Multiple Access (OMA). The authors highlight the theoretical principles of NOMA, multiple antenna-aided NOMA design, cooperative transmission, resource control, and the integration of NOMA with other 5G techniques. They also discuss the advantages of power-domain multiplexing NOMA over other NOMA techniques and identify key research challenges and potential solutions. The paper concludes with design guidelines for NOMA systems and identifies promising research opportunities for future advancements.