Joint radar and communication (JRC) technology is gradually becoming an essential ap-proach to alleviating spectral congestion. Radar and communications systems were designed with common spectral and hardware resources to reduce size, improve performance, reduce cost, and de-congest the spectrum. Various approaches have been proposed to achieve the coexistence of radar and communication systems. This paper mainly focuses on the research directions of radar commu-nication coexistence (RCC) and dual-function radar communication systems (DFRC) in JRC tech-nology. We summarize and analyze the existing research problems in the JRC era. According to the characteristics and advantages of JRC technology, we highlight several potentials in military and commercial applications.