Medium-density fibreboard (MDF), is an engineered wood product formed by breaking down softwood into wood fibres, often in a defibrator, combining it with wax and resin, and forming panels by applying high temperature and pressure.

Large-scale production of MDF began in the 1980s. Its name derives from the distinction in densities of fibreboard. MDF typically has a density of around 800 kg/m³. Low density fibreboard, such as caneite, ranges in density from 160 to 450 kg/m³, while high density fibreboard, such as masonite, has a density of around 1000 kg/m³. The same manufacturing process is used.

MDF is useful in many applications, particularly where particleboard was previously used. It is not useful for outdoor use because it will swell upon contact with water; nonetheless, it has better moisture tolerance than particleboard. Because MDF is fibre-based, it has a remarkably consistent structure. This quality makes it easy to machine or employ in woodworking applications. MDF is often used with melamine or wood veneers.

One contentious issue is the use of formaldehyde resins and the associated health risks. Thus, other resins are being introduced.