This chapter provides an account of the first phase of Pym’s whipping operation, especially the key objective of reducing the numbers of dissenting Conservative Members before the vote on the principle of entry in October 1971. It includes an analysis of the indirect methods of party management that informed strategy, including the maintenance of good relations with the opponents of entry (the anti-Marketeers), and the utilisation of the superior resources of the supporters of entry (the pro-Marketeers). While the Prime Minister, Edward Heath, and his chief ministers and diplomats negotiated terms of entry with European member states, the Whips’ Office monitored the state of party opinion and gathered intelligence on the numbers of ‘pros’ and ‘antis’. This intelligence formed the basis for the Chief Whip’s tactical advice to Heath: first, the use of a ‘fierce campaign of conversion’ to shift party opinion in a pro-European direction, including ‘undecideds’ and ‘waverers’ within the Parliamentary Conservative Party (PCP); secondly, allowing time for the shift in party opinion to take effect, including by postponing the vote of principle until after the summer to allow greater opportunities for pressure to be applied on the ‘antis’ by the combination of ‘the four Cs’—colleagues, constituencies, conscience and Conservative Central Office (CCO); and, thirdly, the necessity of a free vote on the Conservative side to exploit Labour divisions and encourage Labour pro-Europeans to vote with their conscience. The Chief Whip’s tactical approach created the foundations for success. It highlighted the existence of a clear cross-party majority for entry on the Government’s terms, helping to identify the maximum number of Conservative anti-Marketeers, while enabling Labour pro-Europeans to gain a taste for defying their party whip. It proved to be a vital first phase in the process of securing the enabling legislation in 1972.