As a promising downlink multiple access scheme for LTE enhancements and 5G, non-orthogonal multiple access (NOMA) has been attracting a lot of attention in recent years. This paper introduces an overview of the concept, performance evaluation gains, our ongoing experimental trials and current standardization status. The goal is to clarify the benefits of NOMA over orthogonal multiple access (OMA) such as OFDMA adopted by Long-Term Evolution (LTE), also its combination with MIMO is discussed. Using computer simulations, NOMA performance gains are assessed from both link-level and system-level perspectives. Also, our NOMA testbed and the measurement results are explained. Finally, we summarize the current status of ongoing standardization of downlink NOMA, which is currently under study in 3GPP LTE Release 13.