This book investigates several important issues revolving around the psycholinguistic modelling of language proficiency in terms of L2 linguistic knowledge, which is a topic of considerable interest and importance in SLA theories and language testing practice. Four tests including the Elicited Imitation Test, Timed Grammaticality Judgment Test, Untimed Grammaticality Judgment Test and Metalinguistic Knowledge Test are employed to examine the extent to which they provide separate measures of Chinese third-year university students' L2 lingusitic knowledge. The role of four psychological factors – language analytic ability, language learning motivation, language anxiety and learner beliefs – in learners' L2 linguistic knowledge is also explored.