Foreign language and mother tongue presents Kecskes and Papp's cognitive-pragmatic theory of language acquisition in bilinguals and multilinguals. The unique aspects of this theory are that it examines the positive effects of learning a second language on the first language and that it uses multicompetence rather than monocompetence as its starting point. The authors argue that “people who know more than one language have different knowledge of their first language L1 than do monolingual people, and this difference can be due to the effect of subsequent languages on the development and use of L1 skills” (p. ix). This is essentially their first hypothesis. Their second is that the more conscious, analytic, bottom-up approach to L2 learning can have a positive effect on the L1, which was learned using a more subconscious, synthetic, and top-down approach. Their third hypothesis is that because of a so-called common underlying conceptual base, new knowledge and behaviors obtained through the L2 can enhance the real-world knowledge and linguistic skills of learners in their L1 as well as in their L2.