The aim of this article is to explain what the term "languages for special purposes" means and what it does not mean, to outline the rationale for such a branch of language teaching and to indcate some of the problems it poses for syllabus planners and course designers. Four principal types of problems and considerations are identified and discussed: sociological, linguistic, psychological, and pedagogic. Spanish and English versions of the article are printed side by side. (Author/TL)