A key grip is a senior role for an experienced professional on every set. Their responsibilities are extensive and range from supervising grip crews, assessing what equipment is necessary for each shooting location, coordinating the transportation of this equipment and its set up, arranging the general movement and positioning of the camera and collaborating with the director of photography. The key grip relies on the best boy as their foreperson to supervise the grip crew.

Industry myths vary as to the origins of the name "grip". Some say it originated from the early days of the film industry when a set consisted of a director, camera person, assistants and workers. Workers acted as handymen, setting up all equipment needed, working from a kit, container or bag containing their tools. This bag was known as a grip and as the industry evolved and workers began to separate into specialized groups, the name grip stuck with those that worked on rigging. But it is most likely that the term has rail/tram origins, where "gaffers" and "grips" formed an integral part of the US rail transport system in the 19 century. The term "gaffer" is a contraction of "grandfather" or "godfather", used by immigrant Irish-Americans as a term of respect for the supervisor of a gang of working men. A "grip" was a worker whose job it was to grip the electric cable above the tram and transfer it to the new line when the tram reached a junction. As the film industry took off these titles became part of the vernacular. The word "key" when applied to "grip" simply means "principal".

A typical key grip has worked in the industry for years and proved themself worthy of more responsibilities. Those that have attended film school or completed training courses have an advantage as they possess technical understanding of on-set procedures.

Region to region the role and responsibilities of a key grip can differ. In the US key grips supervise the set-up of both cameras and lights, despite unions preventing key grips from touching lights, whilst in places such as Hungary key grips are able to move lights around to their suiting and electricians simply deal with ‘everything that’s connected to a lamp’.