Complexity, accuracy, and fluency (CAF) as measures of language proficiency have been used extensively in assessing second language production in English language studies related to task-based language teaching. The present review adds the following critical elements to the existing body of literature: (i) Provides synthesis and critical analysis of various measures of CAF used in empirical studies and reveals the variation with which the three constructs have been used; (ii) Lays down the most appropriate CAF measures for beginners, intermediates and advanced learners for a valid and robust assessment of oral production in English as a second and foreign language.