A neural network is a computational approach to learning, analogous to the brain. There are three major categories of neural networks. Classification, Sequence learning and Function approximation are the three major categories of neural networks. There are many types of neural networks like Perceptron, Hopfield, Self-organizing maps, Boltzmann machines, Deep belief networks, Auto encoders, Convolutional neural networks, Restricted Boltzmann machines, Continuous valued neural networks, Recurrent neural networks and Functional link networks.