Since Hymes' landmark sociolinguistic paper in 1972, second language researchers and teachers have examined the relevance of communicative competence in acquisition and instruction.  Read Canale and Swain's original 1980 paper, and Savignon's account of communicative teaching:

Canale, M. and Swain, M. 1980. Theoretical bases of communicative approaches to second language teaching and testing. Applied Linguistics 1 (1), 1-47. PDF

Savignon, S. (1991). Communicative Language Teaching: State of the Art. TESOL Quarterly, 25 (2), 261-277. PDF