We had a bit of a problem last year. Hornets hanging around the hive, sometimes grabbing a bee and flying off. We tolerated it but kept an eye on them to make sure things didn't get out of hand. This year we found the new nest, with the queen in it, starting to build. We terminated them on the spot. They chose to set up shop just outside the back door of the house, not gonna happen.
The above links and recipes could be most helpful. Hornets are beneficial in many ways, especially for garden pests, but you have to find the balance of what is good, or threatening in your particular situation.