CubeSat Space Protocol (CSP) is a small network-layer delivery protocol designed for CubeSats. The idea was developed by a group of students from Aalborg University in 2008, and further developed for the AAUSAT3 CubeSat mission that was launched in 2013. The protocol is based on a 32-bit header containing both network and transport layer information. Its implementation is designed for embedded systems such as the 8-bit AVR microprocessor and the 32-bit ARM and AVR from Atmel. The implementation is written in C and is ported to run on FreeRTOS and POSIX and pthreads-based operating systems such as Linux. Support for Mac OS X and Microsoft Windows will be available in version 1.1. The three-letter acronym CSP was adopted as an abbreviation for CAN Space Protocol because the first MAC-layer driver was written for CAN-bus. The physical layer has since been extended to include several other technologies, and the name was therefore extended to the more general CubeSat Space Protocol without changing the abbreviation. The protocol and the implementation is actively maintained by the students at Aalborg University and the spin-off company GomSpace. The source code is available under an LGPL license and hosted on GitHub.