Three research studies conducted at Thai universities involving language testing and courses in General English and English for Academic Purposes (EAP) are discussed. The first study examined the predictive validity of different types of language tests on academic achievement in General English and EAP courses. It found that the test format, as shown in the Matching Cloze Test, may be significant in predicting future academic achievement, and the content of language tests may play a role in academic achievement for each type of language program. The second study showed the direct and indirect relationships between subskills of General English and EAP tests. It found that all language subskills, regardless of content, are significantly related. The third study examined the underlying relationships between General English and EAP tests. It found that EAP tests may predict achievement in EAP programs better than General English tests; the formats associated with each discipline tend to predict academic success in science better than those that are not related to a specific discipline; and there is a common factor shared by the EAP tests, General English tests, and knowledge of the subject matter represented by student grade point average. (GLR)