Abstract: Insulated metal panel siding system for a structure comprising elongated base members and elongated insulated metal panels. The base member is installed along the base of wall framing for the structure and extends across at least two vertical frame members in the wall framing. The base members has a profile running laterally along the upper side thereof. The insulated metal panel is installed on the wall framing running horizontally across the vertical frame members and abutting the base member. The panel has a rigid foam core, an interior metal facing, and an exterior metal facing. The panel also has a profile running laterally along the lower side thereof. The upper profile of the base member and the lower profile of the panel are adapted to allow the base member and the panel to be joined by a tongue-in-groove joint running horizontally across the wall framing.