Compatibility with OS systems can change very quickly, so please check this link from Thomson-Reuters.
EndNote X6 is not officially compatible with Mac OS X 10.11 El Capitan. We will report any major issues and exceptions found to this page. We do not anticipate providing further compatibility updates to fix issues with EndNote X6 and earlier with 10.11.
Yosemite (OS 10.10)
Yosemite.was released about the time as X7.2, which is compatible.
However, you should make sure that your word processor is compatible with your operating system.
Mavericks (OS 10.9)
The most recent version of EndNote is X7, which is designed to be compatible with Mavericks
Download the X7 for Mac (if you don't already have it).
Once you install it, it gives the message "You are currently running version 22.214.171.12413. Would you like to install this update (version 126.96.36.19957)?
Select "Download and Install." You may need to repeat this process until you get to the current update version, (file name X7.2 or 17.2)
See the "Update" tab of this guide if you hae any issues with the update process.
Mountain Lion (OS 10.8)
Officially compatible with X6 and later
Lion (OS 10.7)
Officially compatible with X5 and later
Snow Leopard (OS 10.6)
Officially compatible with X4, X5 and X6. May possibly work with X7, but EndNote does not officially claim compatibility.
Note: When EndNote is not officially compatible with an operating system, it may work for a user, but with some minor glitches or issues. However, support to address those glitches may be limited. If you call Thomson Reuters support when using an operating system with an EndNote version that is not officially compatible, you may be advised to upgrade to the compatible version.
Content updated: October 10, 2014