A method and an apparatus for processing digital broadcast signal are disclosed. The method of processing a digital broadcasting signal in a transmitter includes performing RS (Reed-Solomon) encoding on signaling data containing cross layer information between a physical layer and a upper layer, wherein the signaling data includes a first field indicating a protocol version change of the signaling data, a second field indicating a length of an extension field of a header included in the signaling data, and at least one field indicating a number of ensembles for at least one of a first transmission mode and a second transmission mode, and wherein the ensembles include a collection of services, each of the services being a package of packetized streams of mobile service data, forming data groups including the signaling data and the mobile service data, forming mobile service data packets including the signaling data and the mobile service data in the data groups, transmitting the digital broadcasting signal including the mobile service data packets during slots, wherein the first transmission mode is a mode in which the mobile service data are transmitted while reserving greater than 118 packets out of 156 packets in the slot and the second transmission mode is a mode in which the mobile service data are transmitted while reserving less than or equal to 118 packets out of 156 packets in the slot.