EndNote allows to organise your references into Groups, so you will not need to create separate libraries for subsets of references. Groups appear on the left panel under My Library, and can be renamed or deleted. They can also further organisedd in Group Sets and moved between Group Sets.
The same reference can be added to several different groups, and references deleted from a group will always remain available in All References.
Group Sets allow you to organise your numerous groups:
Smart Groups will automatically add references to a group with specific criteria:
This guide has been based, with permission, on the guide created by the King Edward Memorial Hospital Library.