PKZIP is a compression program that was originally written by Phil Katz and marketed by his company PKWARE Inc.. PKZIP is an abbreviation for Phil Katz's ZIP program.

The first version of PKZIP appeared in 1989. She was a DOS command line program and was distributed as shareware with a registration fee of 25 U.S. dollars. PKZIP 1 used three different compression algorithms, called shrinking, reducing and imploding of which based on the characteristics of a file to be compressed is selected. Although these files were then very common, files in the PKZIP -1 format are now rarely encountered, and many modern unzip programs are no longer able to deal with these compression methods.

In 1993, PKWARE PKZIP 2 out. This version replaced the various compression methods of the first version with one new method, called the Katz deflating. The thus created file format has since been ubiquitous on Microsoft Windows and the Internet -. Almost all files with the zip file name extension are in PKZIP -2 format, and on all major platforms, there are programs to read and write these files.

PKWARE PKZIP developed further, but newer versions of PKZIP format include proprietary compression techniques.

Meanwhile, PKWARE is the global market leader for compression software on mainframe platforms.

In addition, PKWARE 2004 introduced a new product line, called SecureZIP. It is PKZIP encryption with up to 256 bit according to the AES standard. The peculiarity of SecureZIP is that the entire block of data is encrypted and secured not only by a password, there is also the possibility to use x.509 certificates.