BEFORE the smoke of the Irish rebellion of 1798 had cleared, the British prime minister William Pitt was convinced of the necessity of a legislative union between Britain and Ireland. He broached the subject seriously with his cabinet colleague, Lord Grenville, on 2 June and by 4 June the joint post master general, Lord Auckland, an expert on Irish commercial affairs, was brought into Pitt's confidence. Pitt told Auckland that he and Grenville had been able to: ‘see daylight in almost everything but what relates to trade and revenue.' The subject of this paper is to discover how matters of trade and revenue were arranged in the Act of Union and to discuss some of the political difficulties which arose from implementing these arrangements. As the evolution of ministers' thinking is documented, the authorship of some points can be precisely identified and the thinking and tacit economic forecasting brought to light. This paper will suggest that the arrangements were intended to be generous to Ireland and contrasts with an Irish nationalist interpretation of the subject articulated in the early decades of the twentieth century. Then the difficulties that politicians experienced in executing policies within the framework laid down by these articles are considered. The whole vice-regal system of government was by no means guaranteed in the immediate post-Union period as it worked against the chancellor of the Irish exchequer in his attempts to manage Irish public finance.