Getting to know a second language is an act of cognition par excellence. Yet 'Cognitive Approaches to SLA' implies something more than the general research enterprise of SLA. It highlights the goals of cognitive psychologists who search for explanations of second language cognition in terms of mental representations and information processing. It places SLA within the broader remit of cognitive scientists, who—influenced by Marr (1982) to seek understanding at all three levels of function, algorithm, and hardware—work in collaborations involving cognitive psychology, linguistics, epistemology, computer science, artificial intelligence, connectionism, and the neurosciences. It implies the empiricism of cognitive psychology, searching for truths about the world through observation and experimentation and, at times, the rationalism of cognitive scientists who theorize through the construction of formal systems such as those in mathematics, logic, or computational simulation. Much of the research is purely theoretical, but, as in applied cognitive psychology, pure theory can often spin off into important applications, and applied research using longitudinal or training designs in field situations can often advance theory.