Abstract: A method and apparatus for maintaining source control for successive versions of software where modifications are made to an initial version that are not included in the successive versions. When the initial version is received, it is modified and both the initial version and the modified initial version are placed under source control in the form of a source tree. When a new version of the software is received, the invention determines differences between the initial version and the new version and creates a record of differences between the initial version and the new version. The differences are integrated into a copy of the initial version and are then incorporated to the modified initial version, which is then incorporated to a modified initial version to yield a modified new version. In some embodiment of the present invention, the original source tree is retained in case modifications are again made to the initial version.