Computer-aided design, commonly abbreviated CAD, is the use of computer software to create, modify, analyse, document and communicate designs. CAD systems are used to represent physical objects, components, buildings, circuits and other engineered or designed entities digitally. Depending on the discipline, CAD can involve two-dimensional drafting, three-dimensional solid modelling, surface modelling, parametric modelling, assemblies and specialised engineering analysis. CAD replaced or supplemented much manual drafting because digital models can be edited, duplicated, measured and shared more efficiently and can serve as inputs to downstream manufacturing and engineering processes.
Early computer-aided design systems emerged during the development of interactive computer graphics in the mid-twentieth century. Ivan Sutherland's Sketchpad, demonstrated in 1963, is widely regarded as a foundational development in interactive computer graphics and computer-aided design. Commercial CAD systems subsequently developed for aerospace, automotive, architecture and engineering applications. Advances in computing hardware and software made CAD increasingly accessible, moving from expensive specialised systems to desktop and cloud-based applications. Modern CAD systems can represent complex assemblies, maintain design relationships and integrate directly with simulation, manufacturing and product-data-management systems.
CAD models can use several forms of geometric representation. Wireframe models represent objects using points, lines and curves without fully defining surfaces or volumes. Surface modelling represents the outer surfaces of objects and is useful for complex shapes such as vehicle bodies. Solid modelling represents enclosed volumes and can support reliable calculations of mass properties, intersections and manufacturing features. Parametric CAD systems associate dimensions and geometric relationships with model features, allowing a designer to change a parameter and have related geometry update automatically. Feature-based modelling can represent operations such as holes, pockets, fillets and extrusions in a structured history.
Parametric modelling is particularly important in engineering CAD. A designer can define constraints such as parallelism, perpendicularity, tangency, concentricity and dimensional relationships. If a dimension changes, dependent features can update according to the model's rules. This makes it possible to create families of related designs and explore alternatives efficiently. Assemblies allow multiple components to be represented together, with relationships describing how parts fit or move. CAD software can also calculate properties such as volume, surface area, centre of mass and moments of inertia when the geometry and material assumptions are appropriately defined.
CAD is closely connected to manufacturing. A CAD model can be converted into information used by computer-aided manufacturing systems, numerical-control machines, additive-manufacturing slicers and inspection systems. In 3D printing, the CAD geometry may be exported into a suitable manufacturing format and processed into layer instructions. In CNC machining, CAM software can use the model to calculate toolpaths. Engineering drawings can communicate dimensions, tolerances, materials, surface specifications and other manufacturing requirements. The digital model therefore often becomes a central source of product-definition information across design and production workflows.
CAD is used across numerous disciplines. Mechanical engineers use it for components, machinery and assemblies. Architects use architectural CAD and building-information modelling systems to represent buildings and construction information. Electrical engineers can use specialised CAD tools for circuit and PCB design. Civil engineers use CAD for infrastructure layouts and technical drawings. Product designers use CAD for consumer products and prototypes. Industrial designers may combine surface modelling and rendering to evaluate appearance. The appropriate CAD environment depends on the discipline, geometry, collaboration requirements and downstream processes involved.
CAD provides major advantages in precision, repeatability, editability, documentation and design reuse, but it also has limitations. A geometrically accurate model does not automatically guarantee that a design is manufacturable, structurally sound, safe or economical. Designers still need engineering knowledge, material understanding, manufacturing knowledge and appropriate analysis. CAD models can also become complex and difficult to manage if poorly structured. File compatibility can be an issue when exchanging models between different software systems, because translation between formats can lose parametric history, tolerances or specialised features. Version control and product-data management are therefore important in professional environments.
Computer-aided design is ultimately a digital design methodology that connects human design decisions with precise computer representations. It supports visualisation, documentation, simulation, collaboration and manufacturing, and it forms a major part of modern product-development workflows. CAD is distinct from computer-aided manufacturing, which focuses on production processes, although the two systems are closely integrated.
It is also distinct from 3D modelling as a broad concept because CAD generally implies design-oriented tools and structured engineering or drafting capabilities, whereas 3D modelling can include artistic and entertainment applications. Modern CAD increasingly incorporates cloud collaboration, generative design, simulation, automation and parametric intelligence while remaining fundamentally dependent on the accuracy and appropriateness of the designer's requirements and decisions.
