If you have signed up for an EndNote Online account (see EndNote Online) and created a library and use this to collect references when you do not have access to your EndNote desktop version and library you might want to be able to synchronize these two libraries so that they will always consist of the same references. In other words, they will be in sync. Furthermore, when you correct or add something in one of the libraries the other will also be updated.
Why should I have both a EndNote desktop library and an EndNote Online account?
There are mainly two reasons:
Once you have made an EndNote Web account and created a library there you can start syncing your desktop and online EndNote libraries.
Your EndNote Desktop and Online libraries will be synchronized!
If you want to automatize the synchronization you can do this as well.
EndNote training video on how to sync using both Windows and Mac (EndNote X7.1 and later):