In recent years, many educational linguists have emphasised the importance of drawing language learners’ attention to multiword units (i.e., strong collocations, idioms, etc.), because knowledge of such units is believed to help learners come across as fluent, native-like and accurate L2 speakers. A controlled experiment is reported, the results of which support this belief. The question is how learners can be helped to commit multiword units to memory. Insights are borrowed from Cognitive Linguistics, which, contrary to other frameworks, hold that the meaning and the lexical composition of many multiword units is motivated rather than arbitrary. The article surveys experiments that were set up to measure the mnemonic effects of presenting multiword units (especially idioms) as semantically and/or phonologically motivated. The overall encouraging results are explainable by established theories of memory, such as ‘levels-of-processing’ and ‘dual coding’ models. At the same time, the results point to cognitive-style variables that may enhance or dampen the effectiveness of the proposed instructional methods.