The phenomenon of children first producing words and then rapidly expanding their vocabulary is fascinating for both researchers and parents. At first glance, acquiring words and meanings may look relatively simple, but recent studies have revealed that word learning is actually a surprisingly complicated and difficult process. It is unlikely that only one approach can satisfactorily explore that process. The problem of word learning must be examined in many different ways from multiple perspectives. The present paper discusses studies of word learning from 5 different perspectives:(1) word learning biases and applications of those biases,(2) actions and pragmatic aspects of input,(3) developmental data and theoretical issues,(4) the fundamental ability to learn words, and (5) devices for word learning studies. The most important recent studies of word learning in Japan from the present author's viewpoint, mainly from international journals, are reviewed, but important domestic publications are also included and discussed.