Ceiling system

A ceiling system in one embodiment includes an overhead support grid including a plurality of downward facing grid faces and an array of rectilinear grid openings. A plurality of grid-concealment ceiling panels are disposed in the grid openings and arranged diagonally such that corners of the panels are disposed proximate to mating corners of diagonally adjacent panels. Each panel includes peripheral edge portions which extend beneath and at least partially conceal grid faces surrounding the grid opening in which each panel is mounted. In one embodiment, the grid faces are completely concealed. Mating corners of ceiling panels meet at mutually configured chamfered corner surfaces which lie at cruciform intersections between the grid faces. The ceiling panels are arranged in diagonal rows in the support grid. Diagonal rows of filler ceiling panels are provided between diagonal rows of grid-concealment ceiling panels.