Spectrum bands are nature's communication highway which are highly congested now-a-days. To overcome this problem, dynamic allocation of spectrum is under consideration over the current fixed spectrum allotment policy. In dynamic allotment, unlicensed users will be using the channel, whenever they find the channel idle and will immediately vacate the channel if licensed user returns. Handoff is the main feature of dynamic spectrum allotment policy. Also, it has been observed that multiple handoffs may degrade the service quality given to the unlicensed users. For that reason, different optimization methods may be applied for achieving the best possible spectrum allotment during handover so that the better quality of service can be given to the cognitive users with the simultaneous improvement in spectrum utilization. The handoff procedure can be pro-active or reactive type. Pro-active mainly deals with the beforehand preparation of the set of the target channels, while reactive handoff is on-demand approach. Both the styles have their own pros and cons. Depending on the application, any of the handoff technique can be used.