The book investigates the explanatory variables for the passage-reading comprehension performance of Japanese EFL learners and their sentence-reading speed. Following rigorous preliminary studies evaluating the significance of the candidate variables and refining research instruments, a large scale main study was conducted. Regression analyses indicated that syntactic knowledge was the best predictor of passage-reading ability, while vocabulary breadth also contributed to its prediction. Subgroup analyses supported the significance of syntactic knowledge for both higher- and lower-ability readers. Sentence-reading speed was best predicted by the speed of lexical semantic access. The significance of this speed was also consistent across the group division. A subsequent exploratory factor analysis and structural equation modelling of the data indicated that the performances of the participants were best explained in terms of two latent factors: one based on careful text processing power and the other on efficiency of lexical semantic access.