Abstract: Interface is a key concept in linguistics which could be traced back to the famous sign model proposed by de Saussure. After a century's development, linguists have now come back to this interface. In Chomsky's Minimalist Program, a linguistic theory is defined as just a mechanism that satisfies the conditions on the phonetic and semantic interfaces. A part from this interface that plays an explanatory role for the internal structure of language, we can at least identify three other interfaces concerning other aspects of language: the interface between language and thought, the interface between language and culture and the interface between languages. The philosophy of language, the linguistic relativism and translation studies evolve around these three interfaces. With interface as a key concept, we are able to clearly present the characteristics and the basic features of language as a complex system.