Characterization is the sum of measurements and tests applied to a waste package to prove that all its characteristics meet the acceptance requirements drawn up by the authorities in charge of final disposal. If waste producers are in charge of acceptance file presentation, specialized laboratories are involved in testing operations and data interpretation. Because of their knowledge of wastes and the conditioning matrices they have developed, the people in charge of characterization are placed at an interface between producers, repository managers, safety authorities, and research laboratories. Some examples drawn from different fields of activity are given here to illustrate this remarkable situation.