Theories and research on second language acquisition and grammatical theory are reviewed and discussed, especially those concerning the recent interest in understanding the nature of the language-learning faculty. The review includes work in the areas of universal grammar, interlanguage, parameterization of universal grammar, second language learnability, markedness, learning differences between children and adults, other differential learner characteristics and language-processing capabilities, and typological control, and their interrelationships. Problems in research into grammatical theory are also briefly discussed. Four pages of references conclude the document. (MSE)