The present, invention relates to a communication system, a transmitter, a receiver, a communication method, a program, and a communication cable for providing high-speed bidirectional communication while maintaining compatibility. When an HDMI (R) source 71 performs bidirectional IP communication with an HDMI (R) sink 72 using a CEC line 84 and a signal line 141, a switching control unit 121 controls a switch 133 so that, when data is transmitted, the switch 133 selects a constituent signal forming a differential signal output from a converting unit 131 and, when data is transmitted, the switch 133 selects a constituent signal forming a differential signal output from a receiver 82. When bidirectional communication is performed using only the CEC line 84, the switching control unit 121 controls the switch 133 so that the CEC signal output from the HDMI (R) source 71 or the receiver 82 is selected. The present invention is applicable to, for example, HDMI (R).