This book explores the acquisition of tense and aspect by adult second language learners of nine target languages. The author focuses on the association of form and meaning in learners' emerging system of temporal expression. The book provides a survey and synthesis of studies from five perspectives: the meaning-oriented approach, acquisitional sequences, the aspect hypothesis, the discourse hypothesis, and the effect of instruction. In addition, original longitudinal and cross-sectional studies on the acquisition of English by the author illustrate each of the perspectives and explore the importance of research design and analysis in acquisition research.