Teacher-based assessment (TBA) is increasingly being promoted in educational policies internationally, with English language teachers being called on to plan and/or implement appropriate assessment procedures to monitor and evaluate student progress in their own classrooms. However, there has been a lack of theorization of TBA in the English language teaching field, with researchers pointing to much variability, a lack of systematic principles and procedures, and a reliance on traditional, but now outdated, psychometric assumptions. This article provides an overview of some of the current issues in TBA, including its definition and key characteristics, and the complex but significant questions which its implementation pose for our understandings of language, learning, and assessment. (Contains 2 tables, 1 figure and 6 footnotes.)