Cognitive radio (CR) is a promising technology developed to solve the spectrum scarcity problem by opportunistically identifying the vacant portions of the spectrum and transmitting in them, while ensuring that the licensed or primary users (PUs) of the spectrum are not affected. Cognitive radio technology enables the secondary (cognitive) users to use the unused licensed spectrum of the primary users. It is been noted that there is a lot of unused spectrum known as ‘white spaces’ even in commercial broadband and mobile network frequency bands. Cognitive radios can sense and adapt to their environment, utilize the white spaces and improve the spectrum utilization. Medium Access Control (MAC) protocol plays a vital role in spectrum utilization, primary user’s (PU) interference management and secondary user’s coordination in cognitive radio (CR) networks. In this paper we present an overview of current medium access control protocols.