Method for process controlling of plants and plant control systems in an OPC UA based Machine-to-Machine (M2M) network, wherein a plant associated with a plant control system comprises a plurality of interlocked elements of one or more operational unit of the plant, wherein the operation of an operational unit is controlled by the plant control system by means of the elements interlocked to the plant control system, and wherein the plant control system is accessible by an independent process control system in the Machine-to-Machine (M2M) network via network interfaces (16/202), and wherein messages containing signaling data and steering commands are transmitted between the process control system and the plant control system, and wherein the process control system is connected via an OPC UA network comprising OPC UA clients (151/203) and an OPC UA server with at least one programmable logic controller (201/PLC) of the plant control system, wherein the operation of the plant and the operational units are controlled by means of the plant control system comprising the programmable logic controller (201/PLC) via the plurality of interlocked elements, characterized in that the process control system comprises a plant process engine with a library of selectable process control command records for each type of plant control system operatable by the independent process control system, wherein the operation of a corresponding plant is steerable by the process control command assigned to a specific type of plant control system by the selectable process control command records, in that the plant process engine comprises an object linking and embedding unit for process control, wherein the selectable process control commands of the library are converted by the object linking and embedding unit for process control into basic programmable logic controller (201/PLC) commands and/or operations integrated by all programmable logic controller (201/PLC) of the accessible plant control system, in that an OPC UA client (151/203) based on the OPC Unified Architecture is generated each on the process control system and on the plant control system, the transport layer between the OPC UA client of the process control system and the OPC UA client of the plant control system being extended bidirectionally by means of a defined bit sequence containing encoded programmable logic controller (201/PLC) messages, and the OPC UA clients (151/203) being OPC UA network nodes in the OPC UA network with the OPC UA server, in that for steering and controlling the plant, the process control system transmits programmable logic controller (201/PLC) command messages to the plant control system by encoding the PLC command messages for the OPC UA transport layer and transmitting it in the OPC UA transport layer by means of the defined bit sequence, in that the plant control system decodes the PLC command messages by means of the interpreter from the defined bit sequence and transmits the decoded PLC command messages to the corresponding PLC for execution, and in that the plant control system transmits in the OPC UA transport layer by means of the defined bit sequence encoded PLC response messages to the OPC UA client of the process control system, wherein the process control system decodes and processes the PLC response messages from the bit sequence for controlling and steering the operation of the plant.