The popularization of portable media players such as the "iPod," and the delivery of audio and video content through content management software such as "iTunes" mean that there is a wealth of language learning resources freely available to users who may download them and use them anywhere at any time. These resources vary greatly in quality and follow different approaches to learning. This paper provides a taxonomy of podcast resources, reviews materials in the light of Second Language Acquisition theories, argues for better design, and outlines directions for future research. (Contains 2 figures and 1 note.)