Disclosed herein is a bi-directionally raisable drilling rig mast system that includes a drilling rig mast having a bi-directional mast erection connection, a first erection connection positioned proximate a first side of a rig substructure, and a second erection connection positioned proximate a second side of the rig substructure, the second side being at an opposite side of the rig substructure from the first side. The system further includes at least one mast erection apparatus having an upper end that is adapted to be pivotably attached to the bi-directional mast erection connection and a lower end that is adapted to be pivotably attached to the first erection connection for erecting the drilling rig mast from the first side of the substructure, the lower end being further adapted to be pivotably attached to the second erection connection for erecting the drilling rig mast from the second side of the substructure.