Japanese is often called a 'mora-timed' language, and contrasted with 'stress- timed' or 'syllable-timed' languages. The definition of what constitutes mora-timing has undergone several revisions, and a wide variety of experimental evidence both for and against mora-timing has been presented. This article reviews the hypotheses, the means of testing them, and the results of nearly 40 years of experimental work on mora-timing in Japanese, and suggests directions for future work in this area.