In this report, we have described Condor's user-level checkpoint and migration service for UNIX processes. This service was developed with the goals of portability and user transparency in mind, and it has been used successfully to enhance the flexibility of the Condor scheduler and provide forward progress for long running Condor jobs even when machines are available for limited periods of time. It has also been used as a standalone product (i.e., outside of the Condor resource management system) and incorporated into Load Leveler, Load Sharing Facility, CoCheck, Codine and other products.