In agriculture, a harrow is a farm implement used for surface tillage. It is used after ploughing for breaking up and smoothing out the surface of the soil. The purpose of harrowing is to break up clods and to provide a soil structure, called tilth, that is suitable for planting seeds. Coarser harrowing may also be used to remove weeds and to cover seed after sowing.

Harrows differ from ploughs, which cut the upper 12 to 25 centimetre (5 to 10 in) layer of soil, and leave furrows, parallel trenches. Harrows differ from cultivators in that they disturb the whole surface of the soil, while a cultivator instead disturbs only narrow tracks between the crop rows to kill weeds.

There are four general types of harrows: disc harrows, tine harrows (including spring-tooth harrows, drag harrows, and spike harrows), chain harrows, and chain-disk harrows. Harrows were originally drawn by draft animals, such as horses, mules, or oxen, or in some times and places by manual labourers. In modern practice they are almost always tractor-mounted implements, either trailed after the tractor by a drawbar or mounted on the three-point hitch.

A modern development of the traditional harrow is the rotary power harrow, often just called a power harrow.