ZOO is a file extension that is an older format of compressed data archives. Such archives were created on the basis of LZW lossless dictionary compression. This is a method that gives good results when it comes to compression. In favorable cases, it gave up to 80% savings in the occupied disk space than the original.

ZOO files could be found in operating systems based on the Unix kernel. Currently, this format is rare and considered obsolete. Has been replaced with ARC files.