In cognitive radio network, three fundamental tasks are performed by cognitive radio i.e. sensing, learning and reasoning. The importance of learning techniques to be implemented in cognitive radio for the task of learning has been discussed in this paper. Learning techniques for implementation in cognitive radios such as Genetic Algorithms (GAs), Hidden Markov Models (HMMs), Rule-Based System (RBS), Artificial Neural Networks (ANNs) are presented. Merits and demerits of these learning schemes have been tabulated which will help the designers in future to decide about the learning scheme to be used for designing cognitive radio.