The article addresses the long-standing issue over the role of the mother tongue in the foreign language classroom. In the first part it is argued that the mother tongue lays the cognitive foundations for all subsequent language learning. Double comprehension as the basic requirement for learning to take place is explained. The second part is practical. It focuses on two bilingual techniques, idiomatic translations for the clarification of grammatical functions, and mother tongue mirroring which makes grammatical forms transparent and shows their hidden logic. Examples are from various languages, but are especially drawn from Mandarin since non-related languages best illustrate the need for systematic mother tongue support.