A tonneau clamp including a link slidably coupled to tonneau cover; a clamping link pivotably coupled to the link and having a clamping surface; and a handle pivotably coupled to the link and the clamping link and moveable between lowered and upper positions. The handle can be pivotably coupled to the link at a first pivot joint and to the clamping link at a second pivot joint. Handle movement causes the clamping link to pivot relative to the link to raise the clamping surface from an unclamped position to a clamped position in which the clamping surface applies a clamping force against the underside of a ledge of a vehicle cargo box. In the unclamped position the first pivot joint is on a first side of a line and in the clamped position the first pivot joint is on a second side of the line opposite the first side.