This document discusses reliability and validity in language testing. It defines reliability as the consistency of test results and identifies three types: test-retest, parallel-forms, and internal consistency reliability. Validity refers to how well a test measures what it intends to measure. The document lists four types of validity - face, content, criterion-related, and construct validity. It emphasizes that a test needs to be both reliable, in producing consistent results, and valid, in accurately measuring the intended construct, to draw meaningful conclusions from test scores.