A high-level protocol for industrial networks developed in 1979 by Modicon (now Schneider Automation Inc.). Providing services at layer 7 of the OSI model, it defines a request/response message structure for a client/server environment. Modbus runs over various data links including its own Modbus+ token passing network and serial links such as RS-232 and RS-485.

It is widely used with TCP/IP over Ethernet. Individual device networks connected to Modbus+ or serial links hook into Ethernet via gateways for transport over an IP network or the Internet. Modbus is governed by the Modbus-IDA Organization, a merger of the Modbus Organization and IDA Group in 2003. For more information, visit www.modbus.org.