Abstract: A method of and an apparatus for merging a sequence of delta files is described. The delta files together define a series of changes between a base file and an updated file, each delta file defining one or more changes in terms of one or more unique tokens each identifying original data or of one or more reused tokens identifying data reused from the immediately preceding delta file or the base file. The method comprises creating an initial merge structure from the base file and the first delta file in the sequence. A further merge structure is created from the initial merge structure and the next delta file in the sequence by comparing tokens in the initial merge structures and replacing reused tokens in the further merge structure with tokens in the initial merge structure. The initial merge structure is then replaced with the further merge structure so that the further merge structure becomes the initial merge structure.