R5 and R6 are the structural integrity assessment procedures which have been used to assess the fitness-for-service of operating nuclear plants in the UK.The procedures can also be used in other industries.R5 is an established methodology, which is frequently used in the structural integrity assessments of Advanced Gas-Cooled Reactor (AGR) components operating in the creep range.The procedures are also relevant to high temperature plants outside the nuclear power generation industry.R6 is a procedure for assessing defects in components operating below the creep regime.The R6 procedure has been continuously developed since its first publication in 1976 and is accepted, both within the UK and internationally, as a validated procedure for the assessment of structures containing defects under all loading conditions.As both the R5 and R6 are under continuously development, many development programmes have been planned and several of them are in progress.A number of selected future development areas are presented in this paper.