Many studies have carried out on the importance of motivation in the learning of a second language. Besides confirming that traditional motivation theories are positively correlated especially to second language learning, studies have also shown that the application of motivation theories that originated in the West to the learning of languages of the East and West reveals differences in the psychology of learning arising from cultural factors. Newer motivation theories, such as those on self-motivation and learning engagement, in addition to being applied in conventional motivation studies, are also being used in language studies and in second language learning. Drawing on selected studies of the past, this paper will examine the different roles of motivation theories in second language learning.