The Critical Period Hypothesis refers to the idea that the ability to acquire language is related to aging and there is an ideal period of time to attain a language, after which it is no longer possible. Second language learning performance correlates negatively with the age at which the learning begins prior to puberty. Contrarily, among late learners, the correlation of age with learning performance suggests that different mechanisms are affecting adults' proficiency other than maturation. However, it is controversial that this negative correlation between age and learning performance can be attributed to a biologically based critical period for second language acquisition that prevents older learners from achieving native-like competence in phonology as well as syntax of a non-native language.In this literature review, the existence of a critical period for second language acquisition is investigated. It is hypothesised that native-like attainment of second language acquisition is influenced by social, educational and motivational factors such as age of immigration and amount of second language education. The following three literature reviews attempt to demonstrate and support this hypothesis.