This document discusses preference assessments, which are procedures used to identify an individual's favorite reinforcers. There are two types of reinforcers: unconditioned/primary reinforcers which require no learning history, and conditioned/secondary reinforcers which are previously neutral stimuli paired with other reinforcers. Preference assessments should be used because they have high predictive validity and directly measure preference between stimuli. Common assessments include single-stimulus, multiple stimulus without replacement, and paired-stimulus. Proper preparation and procedures are outlined.