A method and transmitting system for processing data are discussed. The method according to an embodiment includes randomizing enhanced data; first encoding the randomized enhanced data to add first parity data for error correction, thereby forming a frame; dividing data of the frame into a plurality of groups, wherein the plurality of groups have a same size; first interleaving data of each group; second interleaving the first-interleaved data; encoding signaling information at a code rate; and transmitting a broadcast signal including the second-interleaved enhanced data and the encoded signaling information. Second encoding on the randomized enhanced data is selectively performed, wherein, when the second encoding is performed, second parity data for error detection are added to the randomized enhanced data. The signaling information includes transmission parameters to indicate whether the second encoding is performed.