EndNote uses RIS files to import bibliographic information from databases, etc., but sometimes Mac users can't consistently open RIS files automatically with EndNote, so they have to associate the file with EndNote every time. To stop this, go to your Downloads folder or wherever you have an RIS file stored, click on any RIS file, then type Command i. In the menu that pops up, look for the Open with option, select EndNote, and then click on Change All. Now it should remember to open RIS files with EndNote.
