This paper sets out to peruse the role of various theories or more precisely, hypotheses invoked in second language acquisition (SLA) research by surveying three empirical studies pertaining to the critical period hypothesis in the SLA of phonetics and phonology. In particular, the three studies reviewed are titled in chronological order as (1) "A critical period for learning to pronounce foreign languages?" (Flege, 1987); (2) "Reexamining the critical period hypothesis: A case study of successful adult SLA in a naturalistic environment" (Ioup et al., 1994); and (3) "Ultimate attainment in L2 Phonology: The Critical Factors of Age, Motivation, and Instruction" (Moyer, 1999).