Millions of individuals worldwide participate in the assessment of their comprehension and production of English. These learners range from young students with non-English-speaking backgrounds enrolled in English-speaking schooling systems to adult learners who are enrolled in English-as-a-second or -foreign language courses. Additionally, assessment of adults may measure [Page 585]English for specific purposes such as higher education, occupational or skilled migration, and citizenship eligibility. This entry focuses on the purposes that English language proficiency (ELP) assessment serves, commonly used ELP assessments and the test takers they serve, and several challenges facing ELP assessment development and measurement.