It is common to encourage foreign-language learners to use their language outside the classroom and to read books and papers, listen to songs and watch films in the foreign language. One of the benefits which are thought to accrue from these activities is that learners can build good vocabularies. It has even been argued that casual exposure to the foreign language of this kind is the "only" way to build a good vocabulary. This paper reviews the published evidence concerning vocabulary acquisition inside and outside the classroom, and reports a series of small and case studies of learners using films, comic books and songs which test in some detail the volumes of lexis gained. It appears that these techniques can lead to very sizeable vocabulary gains but there are some caveats. One is that learners must want to carry out these informal tasks and learn the language. A second is that success appears to be associated with a focus on form, and it is not clear that genuinely incidental exposure to the foreign language results in worthwhile language gains. (Contains 4 tables and 1 figure.)