This document discusses key principles of language assessment, including reliability, practicality, authenticity, washback, and validity. It outlines five types of reliability that can affect language assessment scores: student-related, rater, test administration, test length, and scoring criteria consistency. The document also defines authenticity as how realistic and close to real world the test situation and content are. Finally, it explains there are five types of validity for language assessments: face, consequential, construct-related, content-related, and criterion-related validity.