A tree chipper or woodchipper is a machine used for reducing wood (generally tree limbs or trunks) into smaller woodchips. They are often portable, being mounted on wheels on frames suitable for towing behind a truck or van. Power is generally provided by an internal combustion engine from 2 to 700 kilowatts (3 to 1,000 horsepower). There are also high-power chipper models mounted on trucks and powered by a separate engine. These models usually also have a hydraulic winch.

Tree chippers are typically made of a hopper with a collar, the chipper mechanism itself, and an optional collection bin for the chips. A tree limb is inserted into the hopper (the collar serving as a partial safety mechanism to keep human body parts away from the chipping blades) and started into the chipping mechanism. The chips exit through a chute and can be directed into a truck-mounted container or onto the ground. Typical output is chips on the order of 2.5–5 cm (1–2 in) across in size. The resulting wood chips have various usages such as being spread as a ground cover or being fed into a digester during papermaking.

Most woodchippers rely on energy stored in a heavy flywheel to do their work (although some use drums). The chipping blades are mounted on the face of the flywheel, and the flywheel is accelerated by an electric motor or internal combustion engine.

Large woodchippers are frequently equipped with grooved rollers in the throats of their feed funnels. Once a branch has been gripped by the rollers, the rollers transport the branch to the chipping blades at a steady rate. These rollers are a safety feature and are generally reversible for situations where a branch gets caught on clothing.

The woodchipper was invented by Peter Jensen (Maasbüll, Germany) in 1884; the "Marke Angeln" soon became the core business of his company, which already produced and repaired communal- and woodworking-machinery.

The original chipper design employs a steel disk with blades mounted upon it as the chipping mechanism. This technology dates back to an invention by German Heinrich Wigger, for which he obtained a patent in 1922. In this design, (usually) reversible hydraulically powered wheels draw the material from the hopper towards the disk, which is mounted perpendicularly to the incoming material. As the disk is turned by a motor, the blades mounted on the face of the disk cut the material into chips. These are thrown out the chute by flanges on the edges of the disk.

Commercial-grade disk-style chippers usually have a material diameter capacity of 15 to 45 cm (6 to 18 in). Industrial-grade chippers (tub grinders) are available with discs as large as 4 m (160 in) in diameter, requiring 3,000 to 3,700 kW (4,000 to 5,000 hp). One application of industrial disk chippers is to produce the wood chips used in the manufacture of particle board.

Drum chippers employ mechanisms consisting of a large steel drum powered by a motor. The drum is mounted parallel to the hopper and spins toward the chute. Blades mounted to the outer surface of the drum cut the material into chips and propel the chips into the discharge chute. Commercial-grade drum-style chippers usually have a material diameter capacity of 25 to 60 cm (9 to 24 in).