Modular helmet

A modular helmet (10) comprising: i) a basic helmet (120) to protect from impacts the crown of the head of a user and terminating basally in a rear edge (22) and side edges (20 ); and ii) an extension (140) connectable to said edges, so as to detachably impacts to protect the side and rear of the skull of the user, when adjusted to the base of the hull; characterized in that: iii) said extension is C-shaped and that a ridge (160) connectable centrally over the top of the helmet base, so that can be dismantled, and is arranged, when said extension is set to the helmet base, to secure said extension in the helmet base.