VistA (Veterans Health Information Systems and Technology Architecture), the basis for WorldVistA, is probably the largest integrated HIS in the world. VistA was originally developed and maintained by the US Department of Veterans Affairs for US military veterans.

"WorldVistA was formed to extend and improve the VistA health information system for use outside of its original setting. The system was developed by the U.S. government for use in its veterans' hospitals and outpatient clinics. WorldVistA has a number of development efforts aimed at adding new software modules such as pediatrics, obstetrics, and other functions not used in the veterans' healthcare setting."

"WorldVistA seeks to help those who choose to adopt the VistA system to successfully master, install, and maintain the software for their own use. WorldVistA will strive to guide VistA adopters and programmers towards developing a community based on principles of open, collaborative, peer review software development and dissemination."