This book, reviewing the previous literature on input simplification, elaboration, and enhancement as the three major types of input modification, reports the results of an empirical research about the effects of explicit and implicit lexical elaboration and typographical enhancement alone and in combination on L2 vocabulary acquisition. The book also reviews critically the input modification studies in Iran. Input modification studies, as the book discusses, enjoy a rich theoretical background. Such studies are mostly discussed in the context of second language acquisition theories such as Krashen's Input Hypothesis, Long's Interaction Hypothesis, Schmidt's Noticing Hypothesis, Sharwood Smith's Consciousness- Raising, Language Awareness, Limited Processing Capacity Theory, and Incidental Learning, which the book reviews in brief.