Impact assessment (IA) tools are targeted at decisions and decision-making in theory and in practice. Often described as decision support instruments, most IA are driven by the grand purpose of providing for informed decision-making. In practice this often means IA tends to be more concerned with the information to be provided than with the outcomes of IA and its relevance to the decision(s), and decision-makers(s) to which it should be targeted. Decisions and decision-making are, however, understood in many different ways, and actors involved in decision-making may therefore act widely different with diverse results. Therefore, distinguishing which decisions, and to which decision-makers IA are targeted at, is arguably indispensable to enhance IA effectiveness. Based on an overview of decision-making theory, this paper searches for the understanding of decision and decision-making in IA by exploring how it is conceived in guidance documents. Guidance documents have a prominent role in defining IA practice, and the explicit and implicit recognition of decision-making in guidance is therefore relevant to investigate in order to understand how IA relates to decision-making. With a focus on guidance documents related to the European Union Directive on environmental assessment of plans and programmes, this paper scrutinises four guidance documents and discusses the implications of the identified understandings of decision-making to the practice of IA. The key finding of this paper is that legislation-oriented guidance documents appear to miss to reflect the different forms of decision-making, and primarily depicts decision-making as a single, often timeless and faceless moment. The implications for practice are discussed including reflection on how to describe the nature of decision-making in guidance documents.