Ramesh, K.Ravishankaran, S.Joshi, A.Chandrasekaran, K.2020-03-302020-03-302017Communications in Computer and Information Science, 2017, Vol.750, , pp.336-350https://idr.nitk.ac.in/handle/123456789/7153A conversational agent also referred to as chatbot is a computer program which tries to generate human like responses during a conversation. Earlier chatbots employed much simpler retrieval based pattern matching design techniques. However, with time a number of new chatbots evolved with an aim to make it more human like and hence to pass the Turing test. Now, most of the chatbots employ generative knowledge based techniques. This paper will discuss about various chatbot design techniques, classification of chatbot and discussion on how the modern chatbots have evolved from simple pattern matching, retrieval based model to modern complex knowledge based models. A table of major conversational agents in chronological order along with their design techniques is also provided at the end of the paper. � Springer Nature Singapore Pte Ltd. 2017.Book chapter