1. Introduction Teachers and applied linguists have always been searching for the methods of teaching an L2 that may enable the learners to communicate with least amount of errors. Relying on trending schools of psychology that theorize the mechanism of second language acquisition (SLA), CA, EA, and IL have been proposed. Also, in the frame of these models, researchers (Lado 1957; Corder, 1967, 1981; Stern, 1983; Ellis, 1994, 1997) have attempted to account for L2 errors and explain their causes so as to suggest the appropriate solutions to be applied by teaching methodologists and L2 teachers. CA, pedagogically associated with behaviourism and structuralism, flourished in Europe and North America during the 1950s and the 1960s. Scholars like Fries, Lado, Weinreich, and others were the distinctive researchers in the domain. Later in 1967 when the seminal paper of Corder, The Significance of Learner’s Errors, EA appeared as a new and more welcome model to replace CA on one hand, and to signal the domination of cognitive psychology over behaviorism, on the other. With EA, according to this psychological framework shift, the orientation of pedagogists has switched from teaching to learning (Corder, 1967). Shifting from the interest of accounting for the L2 learner to the brain-based system responsible for the errors has lead Selinker to hypothesize IL in a seminal article entitled Interlanguage in 1972. Psychologically, latent linguistic system of Lennberg (1967), who believed that language acquisition was an age-confined process, was the trigger of Selinker’s IL theory besides his notice of the language of the L2 learner for being colored by forms which are neither of L1 nor of L2. Errors are attributed to different sources related to the basic processes of L2 learning. A detailed account of IL and the previous models are provided in the sections to follow.