This document summarizes key aspects of language proficiency testing. It discusses different types of language tests, ways to describe tests, and factors for evaluating test usefulness. Common tests like TOEFL, TOEIC, IELTS, and CAEL are overviewed in terms of their objectives, constructs measured, and criticisms. The potential impact of testing on teaching and learning, called "washback", is addressed. Critical questions are raised about what tests actually measure and how test use can be made more responsible and fair.