Libchop is a set of utilities and library for data backup and distributed storage. Its main application is chop-backup, an encrypted backup program that supports data integrity checks, versioning at little cost, distribution among several sites, selective sharing of stored data, adaptive compression, and more. The library itself, which chop-backup builds upon, implements storage techniques such as content-based addressing, content hash keys, Merkle trees, similarity detection, and lossless compression. It makes it easy to combine them in different ways. The ‘chop-archiver’ and ‘chop-block-server’ tools, illustrated in the manual, provide direct access to these facilities from the command line. It is written in C and has Guile (Scheme) bindings.