This paper proposes a systematic definition of resistance to program evaluation. A conceptual framework presents the three main dimensions of that phnon: (1) the dynamics of resistance, (2) the persons who could resist and (3) the main phases of an evaluation process where resistance can occur. According to the general model suggested, when person are asked to collaborate in an evaluation, they are faced with a context defined by sources of resistance and facilitative conditions. If their assessment is negative, they will resist. Finally, a specific model is proposed to help identify the conditions that would elicit collaboration from different groups of persons, taking into account various individual and organizational variables.