This study investigated factors that would affect a reader's understanding of the main idea at the global level and explicit and implicit main ideas at the local level. Fifty-seven first-year university students taking a college reading course took a comprehension test on an expository text. Statistical analyses revealed that text structure had a moderate effect on the reader's understanding of the global main idea; only a weak correlation existed between comprehension of the global main idea and local main ideas, particularly the explicit main idea. Analysis of the local main idea's textual features suggested that identification of the explicit main idea was affected by the degree of explicitness, which was measured in terms of sentence structure, position in the paragraph, and the number of points in the sentence. Analysis of textual features associated with implicit main ideas indicated the complex role of example in illustrating the main idea. The study offers some practical implications for college reading curriculum and instruction as well as textbook writing. (Contains 5 tables.)