The text and accompanying workbook are designed to help second language teachers explore theories of language teaching and learning, deriving a set of hypothesized principles for classroom teaching based on the concept of proficiency and suggesting classroom techniques using them. The first two chapters outline and expand on both theoretical and practical insights into the nature of proficiency. Chapter 3 presents the hypothesized principles. The fourth chapter reviews research on the role of context in comprehension and production of discourse, and the fifth offers suggestions for contextualizing listening and reading practice. Chapters 6 and 7 provide guidelines for contextualizing practice in speaking and writing and for activities integrating all language skills. In chapter 8, the treatment of culture in language teaching is addressed. Chapter 9 presents formats for proficiency-oriented classroom testing, and the final chapter illustrates how daily lesson planning can be proficiency-oriented. Appended materials include American Council on the Teaching of Foreign Languages (ACTFL) proficiency guidelines, samples of error coding procedures for written work, and forms useful for course evaluation. The workbook contains exercises keyed to each chapter. (MSE)