The important role collocations play in English L2 vocabulary depth learning and development has attracted researchers’ attention. Unlike attempts to measure vocabulary breath, vocabulary depth (i.e., collocational knowledge measurement) has received less attention by language researchers and is under practiced by language teachers. To understand why this is the case, empirical studies using collocational knowledge measurement instruments published between 2000 to 2017 and indexed in Web of Science, EBSCOhost, Scopus and ERIC were targeted for review and analysis. To bring the importance of measuring collocational knowledge to the forefront, this paper: 1) reviews the research on instruments used to measure L2 learners’ receptive and productive collocational knowledge; 2) attempts to unpack the relationship between collocational knowledge and other linguistic constructs (e.g., speaking fluency and reading comprehension); 3) discusses the effect of language learning tasks (e.g., form-focused and meaning-focused learning) on collocation acquisition; and 4) from the point of view of a language instructors, discusses the practical utility of the previously developed and implemented instruments.