This paper explores the foundations of the theory of exploitation as the unequal exchange of labour (UEL). The key intuitions behind all of the main approaches to UEL exploitation are explicitly analysed as a series of formal axioms in a general economic environment. Then, a single domain condition called Labour Exploitation is formulated, which summarizes the foundations of UEL exploitation theory, defines the basic domain of all UEL exploitation forms, and identifies the formal and theoretical framework for the analysis of the appropriate definition of exploitation.
