Hellfest (French pronunciation: [ɛlfɛst]), also known as Hellfest Summer Open Air, is a rock festival focusing on heavy metal music, held annually in June in Clisson, France. Its high attendance makes it the French music festival with the largest turnover. It is also one of the biggest metal festivals in Europe and the biggest to exist in France. It has been referred to as "the most diverse extreme metal festival in the world," and is a favorite of many musicians to perform at. It originated in another music festival, the Fury Fest, held from 2002 to 2005, in different areas of Pays de la Loire.

=== Early years === The first association was created in 2000 in Clisson as "CLS CREW", in order to organize concerts of hardcore and punk in the region of Nantes. The success of these concerts made it possible to launch the first festival in June 2002, named Fury Fest. It gathered 400 people to attend Agnostic Front in Clisson at the sports complex of Val-de-Moine. The festival continued the following years. It attracted 7,000 people to attend concerts of Sick of It All and Youth of Today (in) in 2003. The format changed to two days. Because no room was available in Clisson, the Hall of Trocardière (Rezé) hosted the second edition. The organization of the festival also changed: the "MAN.IN.FEST" association was created to take charge of the organization. In 2003, the festival had reached €30,000 in profit, allowing Benjamin Barbaud, one of the founders, to become an employee of the structure. In 2004, the festival moved to Le Mans and took place in the halls of the 24 Hours circuit where it attracted 21,000 spectators for bands such as Slipknot and Soulfly. After a deficit in 2004, the 2005 festival inherited liabilities so that the organizing team decided to give the rights of the festival to other promoters in order to focus on organization.