In this paper, an overview of ATC radar has been provided. ATC radar is the tool used by ATC to control airspace and provide safe and efficient air travel. Currently, there are two classes of ATC radar: ASRs and ARSRs. The S-band ASRs and L-band ARSRs are optimized to perform real-time monitoring of airspace in the terminal and en route environment, respectively. ATC radar employs both PSR (skin track) and SSR (aircraft transponder). A general discussion of PSR and SSR for these radar classes was provided. Weather detection design issues for ATC radar were also discussed. Finally, a look into the future of ATC radar was provided.