Over the past three decades, a growing number of different theories in second language acquisition field have come out in an effort to provide explanations as to how language learning takes place, to figure out what variables are effective for second language acquisition as well as to offer guidance to mass second language learners and language teachers. Because behind every teaching approach exists certain kind of theory of language acquisition and good theory in turn can help students master language skills in an effective and efficient way.Each theory is considered to have contributed to the field by highlighting a specific aspect of the language acquisition process. Second language acquisition theories are intrinsically related with various disciplines such as applied linguistics, psychology, education, sociolinguistics, neurology, etc. Considering the impossibility to elaborate all second language theories, I will focus on sociocultural theory and bottleneck hypothesis in second language acquisition. There is an overview which follows the introduction to the Sociocultural Theory and Bottleneck Hypothesis and its contribution to second language acquisition respectively, and then I will evaluate them to see their contributions to the SLA disciplinary development.