The science and practice of selecting information from populations in a manner that allows defensible inferences to be drawn from those data. Target sample/population of interest: person= sampling unit. Aim to ensure results can be reflective of, and can be applied to the population that you are describing. Non probability sampling: nonrandom bias for selecting sample using judgement criteria. Quota sampling: selecting sample elements according to a predetermined distribution across certain categories, there is still diversity, form of stratified sampling but not random, cannot predict probability of being chosen. Convenience sampling- sample who is convenient to get. Snowball sampling- starts with convenience sampling or a group that have something in common and then increase size of group by having participants refer other participants. Purposive sampling- selecting all sample elements according to a certain criterion. Quota sampling-selecting stratified sample but in a nonrandom way (selecting by more than one variable ex. Theoretical sampling- selecting based on a philosophy of qualitative research.