Evaluation theories: from whom and about what? We will follow a hypothesis from Shadish, Cook and Leviton (1991). According to them, there are “spontaneous theories” of evaluation among practitioners and “academic theories” among the literature. In this paper, we will try to describe, compare and discuss these two kinds of theories. We will first examine the “spontaneous theories” of evaluation. Indeed, we found traces of them in the acts and discourses of a sample of professional evaluators that we met during a doctoral research. We will describe the form and content of these theories before examining their origin and development. We will then describe the “academic theories” of evaluation developed in the literature (form, content, origin and development). We will finally discuss the advantages and limits of each kind of theory and try to understand how they circulate and how they can enrich each other.