OK, it's not really a surprise. Netflix tends to renew all of their shows, and this one has been getting particularly good ratings, but that just means we're all the more excited.
There are some changes coming, however, in terms of the show's leadership. Drew Goddard and Steven DeKnight are stepping down as showrunners and will be replaced by Doug Petrie and Marco Ramirez who worked closely with DeKnight and Goddard on the first season.
Also read: The Librarians, Season 4HDClosed Captioning