A patent family is a set of either patent applications or publications taken in multiple countries to protect a single invention by a common inventor(s) and then patented in more than one country. A first application is made in one country – the priority – and is then extended to other offices.
An overview of the three main types of patent family based on an example
This broader definition of a patent family takes domestic application numbers as additional connecting elements and includes documents having the same scope but lacking a common priority.
In Espacenet a patent family is defined as comprising all documents having exactly the same priority or combination of priorities.
Patent Families in the Thomson Scientific World Patents Index (WPI) draw together patents covering the same invention. Their relationship is defined by the priority or application details claimed by each document.