This article analyses the functions and disciplines of the cumulative injury assessment under Article 3.3 of the Agreement on Implementation of Article VI of The General Agreement on Tariffs and Trade 1994 (‘Anti-Dumping Agreement’). Since the text calls for cumulation only if ‘appropriate’, this article refers to the treaty context, the preparatory works, the precedent dispute settlement cases, as well as the relevant practice of the WTO member countries, to understand the purpose of cumulation and to give meaning to this key element of the treaty text. The analyses lead to the interpretation of Article 3.3 that, in order to ‘determine’ that cumulation is ‘appropriate’, an investigating authority needs to identify the factual circumstances where the subject products from all of the cumulated sources compete so intensively that the market position of dumped imports from all but one of the cumulated sources can be realistically taken over by the imports from one remaining source rather than the domestic like products. This article later calls such circumstances the ‘competitive overlaps’. While Article 3.3 gives an authority a certain degree of discretion, the authority’s determination must be based on the factual elements relevant for the competitive overlap in each case. GATT, WTO, Anti-dumping Agreement, anti-dumping, cumulation, cumulative assessment, conditions of competition, competitive overlap