The patent family refers to a group of patents registered in several countries to protect an invention. The patent application is done in one country and then obtains priority. This priority is then extended to numerous countries. A patent family is thus one invention which is patented in several countries by one inventor or group of inventors.
All of the patents in the patent family are linked by priority numbers which are shared and which have the priority dates in common. The idea of a patent family came as far back as 1883 with the Paris Convention. The relationship between the patent application document and the priority determines the description of the patent family. The patents in the same patent family can have differences in the scope of protection because of priority dates and the claims accepted in applications by the various patent offices around the world.
When a patent search is conducted one can also search for patent families. It should be noted that although database organisers do everything they can to ensure uniformity and thus the ability to retrieve all the documents related to a patent family, that some documents may still not be retrieved. When viewing the above one can see that there is a correlation between a patent family and the normal human family. Every document is related to another is some way or another and connected because of priorities. One should note that in a patent family there are also active and non-active priorities. The simple patent families do not include the non-active priorities, but more complex patent families may very well.
If you want to ensure that all documents related to a patent family are retrieved it will be best to make use of patent attorneys familiar with the various patent databases and how to search for complete patent families.