Injection moulding is the process that moulds plastic through heat and pressure, by injecting molten plastic polymer into the desired mould.

Injection moulding is the most commonly used process for moulding plastics because it gives a good surface finish and can be used for very complex mouldings. Injection moulding, although requiring a substantial capital investment, becomes very economically viable in mass production and gives a very low unit production cost. Injection moulded plastics are invariably thermoplastics because thermosetting plastics assume their final shape through heat and so can not be moulded with this process.

Familiar products manufactured by injection moulding include: computer enclosures, milk crates, CD cases and mobile phones.

The plastics that are used in injection moulding include: polythene, low density polyethylene (LDPE), high density polyethylene (HDPE), polystyrene (PS), polypropylene (PP) and acrylonitrilebutadienestyrene (ABS).