Much confusion permeates discussions of the domestic support provisions of the WTO Agreement on Agriculture and in the ongoing Doha negotiations. The paper clarifies some conceptual distinctions with a view to dispelling some confusion, enhancing communication, and facilitating the representation of domestic support provisions in economic analysis. It distinguishes between classification of policy measures and measurement of support, between measures and support, among measures classified in various categories, between applied support and commitments, and between applied support that counts towards commitments and applied support that does not. It highlights certain issues, including the role of criteria in classifying policy measures (such as those labelled green box or blue box measures), the role of de minimis rules in measuring certain applied support (such as Current Total AMS), and how the time specificity of applied support may complicate analysis of domestic support provisions. It introduces schematic charts to complement the verbal exposition of classification and measurement rules under the Agreement on Agriculture and as suggested in the 2004 Framework of the Doha negotiations on agriculture.