An historical overview of research on second language acquisition considers research topics examined in observational/longitudinal studies and experimental studies. The questions that have reappeared across both observational and experimental studies concern: (1) whether second language learning is the same or different from first language learning, (2) the importance of interference/transfer, and (3) whether there is an optimal age effect for success in second language learning. Several explanations are noted for similar patterns emerging in the acquistion/production of both first and second language learners. If one accepts the proposition that there are strong similarities between first and second language learning, a second area of analysis is the role the first language has in second language learning. Contrastive analysis studies have been conducted to examine differences between first and second languages in order to predict where errors would be committed. The mechanisms of interference and transfer between the first and second languages have been the topic of debate. The conversational analysis approach has been utilized to investigate an optimal age for language learning. It is suggested that the whole area of adult learner conversation needs much more exploration before strong claims can be made about discourse analysis as an explanation for adult vs. child success in second language learning. (SW)