There are three main types of validity that are used to evaluate selection techniques in hiring: criterion-related validity, which measures how well a technique predicts job success; content validity, which measures how well a technique samples the key skills for a job; and construct validity, which compares a technique to other validated methods. Common selection techniques include resume reviews, reference checks, interviews, cognitive tests, work samples, integrity tests, and personality assessments, each with strengths and weaknesses related to validity, cost, and legal issues. Employers must consider reliability, validity, and anti-discrimination laws when designing selection processes.