ISA-95 defines five functional levels, assigns Level 4 to business planning and logistics, and defines what crosses the boundary between Level 3 manufacturing operations and Level 4 enterprise systems [S1][S2][S5].
The model covers physical processes, sensing and manipulation, supervisory control, manufacturing operations management, and enterprise planning, providing a shared structure for ERP, MES, SCADA, DCS, PLC, and field-device responsibilities [S2][S5].
Five ISA-95 levels and their decision horizons
ISA-95 divides manufacturing into Levels 0 through 4: Level 0 is the physical process, Level 1 handles sensing and manipulation, Level 2 performs monitoring and supervisory control, Level 3 manages manufacturing operations, and Level 4 handles business planning and logistics [S1][S3].
These horizons identify the pace of the decision, not a guaranteed response time for every installed system.
Level 0 and Level 1: the process and its control interface
Level 0 contains the physical manufacturing process, while Level 1 contains the sensors, actuators, and control devices that measure and manipulate that process [S1][S4]. In a bottling line, for example, the bottle-filling equipment and product flow are Level 0, while the level switch, flow transmitter, control valve, and valve actuator are Level 1 assets [S4].
A temperature-controlled reactor gives the same distinction a more useful form.
This distinction matters when engineers build a functional hierarchy. Treating every field device as Level 0 mixes measurement, manipulation, and physical transformation into one category, obscuring where the control loop ends and the production process begins [S2][S6]. The model also does not prescribe a particular sensor technology or control protocol, because ISA-95 is a logical integration framework rather than a hardware implementation specification [S5].
Level 2: supervisory control and operational visibility
Level 2 combines monitoring and supervisory control, commonly implemented through SCADA, HMI, and DCS functions that present process state, alarms, trends, and operator control [S2][S3].
Level 2 is broader than a display screen. This avoids classifying systems by brand or screen count and instead evaluates the decision they perform.
Published implementations are not perfectly uniform. Some descriptions place PLCs and DCS systems at Level 2, while other reference arrangements place the controller at Level 1 [S5]. The defensible rule is functional: if the device executes closed-loop manipulation against the process, it supports Level 1; if it supervises coordinated equipment and process states, it supports Level 2. The classification should be recorded in the plant's functional design rather than inferred from vendor terminology.
Level 3: manufacturing operations management
Level 3 manages the production operation across production, quality, maintenance, and inventory activities, making MES the typical representative but not the only implementation [S2][S4].
The four activity areas provide a practical scope check for Level 3 systems. Production operations execute and report production, quality operations handle inspection and conformance, maintenance operations coordinate work execution, and inventory operations track materials in process [S2][S4]. A system that merely stores historian data may support operations without owning all four MOM responsibilities.
Level 4: business planning and logistics
Level 4 owns business planning and logistics, including orders, inventory, plant scheduling, finance, and demand-related coordination, with ERP as the common implementation [S2][S4]. In an automotive plant, Level 4 can plan how many vehicles a plant should build, allocate material, and balance order demand, while Level 3 determines how the available equipment and labor execute that plan [S3].
The principal ISA-95 interface crosses the Level 3 to Level 4 boundary: production schedules and related instructions move downward, while production-performance, material, and logistics information move upward [S2][S5]. This boundary is more useful than placing a hard line around MES, because many plants distribute dispatching, inventory, maintenance, and recipe functions across more than one application [S2].
Level 4 does not directly own a valve command or a reactor alarm. The decision horizon also changes from days or months at Level 4 to seconds or sub-seconds at Levels 2 and 1 [S2][S5]. An order received in ERP therefore should not enter the same execution path as a high-speed controller interlock.
Comparing the main level assignments
The most reliable ISA-95 classification method compares four criteria: the physical activity performed, the decision horizon, the system that owns the output, and the direction of data exchange. The model is useful for defining ownership and exchange between functions, not for enforcing a universal equipment inventory [S2].
The comparison shows why system names are insufficient. A system labeled “SCADA” may perform Level 2 supervision, Level 3 production reporting, or both, while a DCS can support Level 2 supervisory control without owning the manufacturing plan [S5]. ISA-95 classification should therefore follow the activity and information ownership, not the product label.
Where real plants diverge from the diagram
Real plants rarely reproduce a clean five-level pyramid because one platform can perform functions at several levels, and legacy systems often cross nominal boundaries [S2][S6]. A historian may combine Level 2 process-state visualization with Level 3 production reporting, while an ERP module may exchange production status directly with a controller gateway rather than through a separate MES [S2].
Three practical divergences recur in plant implementation. First, Level 3 functions can be split across MES, SCADA, historians, batch management, recipe management, and maintenance systems rather than concentrated in one platform [S5]. Second, control responsibilities may be divided between PLCs, DCS systems, edge controllers, and field devices, making the published Level 1 versus Level 2 boundary vary between references [S5]. Third, an enterprise interface may send more than production schedules and receive more than performance totals, including material, quality, maintenance, and inventory exchanges [S2][S5].
The model still delivers value when treated as a map rather than a physical network diagram. Flexware recommends using ISA-95 to define which system owns each data element and how systems exchange it [S2]. For brownfield projects, that means documenting the actual activity, system owner, interface, and time horizon for every production and enterprise decision.
Sourcing, standards, and project boundaries
ISA-95 is the International Society of Automation standard for enterprise-control system integration and is published internationally as IEC 62264 [S1][S2]. Part 1 covers models and terminology, Part 2 covers objects and attributes for enterprise-control integration, Part 3 covers manufacturing operations management activity models, and Part 4 covers objects and attributes for manufacturing operations management integration [S5].
The 2025 Part 1 edition is ANSI/ISA-95.00.01-2025 and aligns with IEC 62264-1, including a revised figure highlighting the boundary between enterprise and manufacturing functions [S2]. ISA lists eight parts in total [S5]. The framework also provides object models for equipment, materials, personnel, and production, and B2MML is an XML implementation commonly used for ERP-to-MES messaging [S2].
ISA-95 itself does not prescribe which software performs each function. B2MML is one implementation of the model, while OPC 10030 treats ISA-95 as an abstract logical model for organizing data exchange [S5]. The standards and model should therefore guide interface scope, terminology, and ownership, but not replace control-system design, cybersecurity architecture, or equipment-specific engineering standards.
For the next implementation step, create a one-page level register for each major line, identify the Level 3 and Level 4 owner for production schedules and performance results, and record at least one real asset chain from Level 0 process equipment through the Level 1 sensor and actuator to the Level 2 controller and Level 3 operation record [S2]. This creates a verifiable boundary that can be tested against plant data rather than a diagram copied from a reference model.