EPICS is not a single monolithic piece of software, but a collection of software tools that work together to help create a control system. Different parts of EPICS were developed at different places, and are distributed under different licenses depending on the originators of the software, which in turn will usually depend on the requirements and policy of the laboratory or other organization that sponsored the work.
All the EPICS code that was written at Argonne or in collaboration between Argonne and Los Alamos and distributed by APS is now all available under the EPICS Open license.
The EPICS Open license was derived from the old and more restrictive EPICS Base license and includes certain wording required by the the US Department of Energy (which is why we can't just use something like the modified BSD license). It is intended to comply with the Open Source Definition, but has not been submitted for approval to the OSI panel.
For APS to be able to redistribute software written elsewhere, the licensing terms for that software must be explicitly stated and permit us to do this. Modifications to EPICS Base or other APS-hosted tools can only be accepted after APS has received a signed Grant of License.
If you develop EPICS software as part of your job, your software is probably owned by your employer, and as a result you'll probably have to get approval from your management to license and distribute it. If any part of the code was developed elsewhere and does not already have the EPICS license attached to it then you probably need to obtain permission for licensing from the original author. If any code you're using is already licensed under a different license such as the GNU GPL or LPGL then you'll need to consult that license and probably a legal expert about what you can and can't do with it. This section assumes that you have already done that. This is not legal advice, I am not a lawyer.
To use the EPICS Open License for your own program, download and copy the LICENSE Text file into the top level directory of your distribution and edit the five words inside <CHEVRONS> as appropriate for your project. You should also download the license header file, edit it as before and insert a copy of this into every significant source file to which the license should apply.
Questions about the licensing or other related administrivia should be emailed to Andrew Johnson <anj_at_aps.anl.gov> (replace _at_ with the @ symbol in that email address).
EPICS Base versions between 3.13.7 and 3.14.4 were originally distributed under the EPICS Base License Agreement, which was not an Open Source license. This was a legal agreement between the Licensee and the copyright holders which allowed APS to control who could obtain copies of the EPICS Base software, as required under the EAR-99 classification which EPICS received several years before. As of February 2004 this EAR-99 classification no longer applies, so we have changed the terms of the license to distribute Base under the EPICS Open license.
Here is a map showing the approximate locations of the EPICS sites around the world as at September 2003. Appologies for my poor geography, I'm sure there are lots of dots in the wrong places!