Spectrum sensing is the underlying advance of the cognitive radio procedure where the radio detects the spectrum to find inactive parts of the spectrum. A cooperative spectrum sensing scheme utilizing spread spectrum various access and improved piece trade instrument which gives numerous sensing updates to a solitary piece demand in the cognitive condition has been created. At the point when left unused the radio spectrum licensed to lasting users, gets squandered. The requirement forced on remote correspondence by the confinement of frequency spectrum is exceptionally overwhelming. The demand for extra spectrum is becoming quicker than innovation can build spectrum efficiency. As a result, costs increment because of higher multifaceted nature for pressing most extreme information rates out of the constrained spectrum. This paper reviews Cognitive Radio Dynamic Channel Selection and Opportunistic Channel Selection