An increasing number of works on chess problems are being made available in downloadable electronic form. These books are either out of copyright or have been approved for presentation in this form by their authors. Eventually it seems certain that most past literature on chess problems will become accessible in this form. Some of this material is in PDF format for which you need to install Adobe Reader if you haven’t already got it. Also some files are compressed and need to be “unzipped” after downloading. If your operating system doesn’t include zipping/unzipping facilities as standard, you will need to download and install a third-party program such as WinZip. We also include here sites that promote works in the form of Bio-Optical Organised Knowledge Systems (BOOKS)!