The aim of this study is to investigate the relationship between frequency and language acquisition from many perspectives including implicit and explicit instruction, frequency effects on morpheme acquisition in L2, the relationship between frequency and multi-word constructions, frequency effects on phonetics, vocabulary, gerund and infinitive constructions, bitransitive constructions, and so on. In his impressive article on frequency, Ellis (2002a) asked this crucial question about the relationship between frequency and SLA: "How exactly does the frequency of patterns in the input affect acquisition?" Another fundamental question that needs to be answered is: "What purpose does frequency serve in language acquisition?" In addition, frequency and range are said to be the most salient criteria for determining the general usefulness of a word (Koprowski, 2005). Moreover, both corpus and experimental data suggest that frequency has significant effects on second language acquisition. These questions and arguments, which constitute the foundation of frequency studies in second language acquisition, led and guided this study. This annotated survey, summarizing the studies on frequency effects on L2 learning, shows that there are still lots of ways to go with research on the relationship between frequency and second language acquisition in the literature. Some pedagogical implications are discussed with recommendations for the stakeholders of foreign language contexts (i.e. curriculum designers, coursebook writers, language teachers and learners).