The electromagnetic spectrum is a characteristic asset. The present spectrum authorizing plan is not able to oblige quickly growing demand in wireless communication due to the static spectrum allocation strategies. This allocation prompts increment in spectrum scarcity issue. Cognitive radio (CR) technology is a propelled remote radio design which aims to expand spectrum utilization by distinguishing unused and under-used spectrum in rapidly evolving environments. Spectrum sensing is one of the key stratergy for cognitive radio which detects the presence of primary client in authorized licensed frequency band utilizing dynamic spectrum assignment policies to utilize unused spectrum. In many areas cognitive radio frameworks coexist with other radio frameworks, utilizing the same spectrum yet without creating undue interference. The most simple and easy to implement sensing technique is energy detection. The paper focuses on common techniques on Spectrum Sensing.