This document discusses principles of language assessment. It defines key terms like assessment, tests, evaluation, and measurement. There are formal and informal assessments as well as formative and summative assessments. The purposes of different types of assessments are also outlined, including achievement tests, diagnostic tests, placement tests, and proficiency tests. Principles of effective assessment are discussed, such as reliability, practicality, validity, washback effect, authenticity, and addressing different types of reliability.