2.4. The development of a geological disposal facility is likely to take place over several decades. These long timescales, the large volume of information (to be acquired from site characterization and other activities that will support the safety case) and its diversity make it essential to subdivide the programme into a series of steps so that the work can be performed, reviewed and assessed in manageable ‘'packages’' with the overall objective of exercising proper control throughout the programme. This comprises the step by step process. Operators of geological disposal facilities may define a number of steps in their own programme. However, in this Safety Guide the step by step process refers to the steps imposed by the regulatory and political decision making processes.