This is a description of how to create a Single System Image (SSI) cluster of virtual User-Mode Linux (UML) machines. After explaining how to use the pre-built SSI/UML binaries, this document demonstrates what an SSI cluster can do. Then it shows more advanced users how to build their own SSI/UML kernels, ramdisks and root images. Following that, it provides an overview of how to move to a hardware-based SSI cluster. It concludes with a set of links and an invitation to contribute to the SSI Clustering project.