This book is based on a series of four lectures, presented at National Taipei University, Taiwan, which reviewed the fundamentals of second language acquisition theory, presented original research supporting the theory, offered counterarguments to criticisms, and explored new areas that appeared to have promise for progress in both theory and application. The four chapters are: (1) "Principles of Language Acquisition" (theory and applications); (2) "Free Voluntary Reading: Still a Very Good Idea" (e.g., research on free reading, light reading as a bridge, and motivating students to read); (3) "Current Issues and Controversies: Does Grammar Teaching Work? What About 'Comprehensible Output'?" (the role of grammar and comprehensible output); and (4) "How Reading and Writing Make You Smarter, or, How Smart People Read and Write" (e.g., how people get smart, research on learning by problem solving, reading and cognitive development, and writing and cognitive development). (Contains approximately 190 references.) (SM)