Background and Aims This paper is an introduction to three concurrent, parallel group, randomised trials of primary surgery for patients born with complete unilateral cleft lip and palate (UCLP) outlining the development and performance of the project by ten North European cleft teams: Aarhus/Copenhagen (Denmark), Bergen/Oslo (Norway), Gothenburg/Linköping/Stockholm (Sweden), Manchester/Belfast (UK) Method The three trials included patients born with complete unilateral cleft lip and palate (UCLP). One surgical protocol was defined to serve as a common method in each trial against which the established local protocols were compared. The common surgical protocol was lip and soft palate closure at 3-4 months and hard palate closure at 12 months. Trial 1 compared this with only a variation in timing: hard palate repair at 36 months; Trial 2 with lip repair at 3-4 months followed by hard and soft palate closure at 12 months; and Trial 3 with lip and hard palate repair at 3-4 months and soft palate repair at 12 months. The primary outcomes at age 5 were speech and dentofacial development, with a series of perioperative and longer term secondary outcomes. Potential harms such as bleeding, airway problems, dehiscence, and need for further secondary revision are included. These will be described in more detail in the series of reports following on from this introductory paper. Results Recruitment of 448 infants took place over a 9 year period with high subsequent retention of participants in each trial. The five year results for the trials are now available. The following numbers of patients were randomised in each trial (Common Arm: Other Arm) Trial 1 (75: 73) Trial 2 (73: 78) Trial 3 (70: 79). The numbers analysed for each outcome and time point will be described in the series of reports. Conclusion The series of reports that follow this introductory paper present comparisons at age 5 of surgical outcomes, speech outcomes, measures of dentofacial development and appearance, and parental satisfaction. Trial registration: ISRCTN29932826 Funding : Partial support from the University of Manchester and University Hospital Rikshospitalet and Bredtvet Resource Centre, Oslo. Additional partial support for the research assistant was provided by grants from the European Commission Biomed II and Framework V Programmes and the Swedish Research Council for Health, Working Life and Welfare, (No 2011-1443). Key Words: Randomised control trials, Multicentre study, Scandcleft, Unilateral Cleft Lip and Palate, Palatal surgery. Running head: Scandcleft, planning and management.