A method and apparatus for transmitting broadcast signals are discussed. The method can include generating an input stream having plural input packets, link processing the input packets in the input stream to generate link layer packets, physical processing the link layer packets into the broadcast signals, and transmitting the broadcast signals. The link processing can include generating a payload of a link layer packet by encapsulating either a segment of one input packet or concatenated input packets, generating a header of the link layer packet including a base part, the base part including a first field which indicates whether the payload includes either the segment or the concatenated input packets, and inserting the header in front of the payload.