A clog is a type of shoe or sandal with a rigid, often wooden, sole. Clogs were widely worn by workers as protective clothing in factories, mines and farms. In more developed countries they have been replaced by steel toe-capped boots, or by rubber boots. In the strictest sense, the term refers to any article of footgear with (at the least) a wooden sole; traditional examples include Dutch klompen, French sabots, and Japanese geta, while more modern versions include Dr. Scholl's "exercise sandals".

In a broader sense, it also applies to any article of footgear that is designed, either partially or completely, in imitation of some form of traditional or practical clog, but with a cork, rubber, or plastic sole, but usually excludes non-wooden platform shoes intended for fashion rather than practicality, in which neither the sole nor the upper is patterned after European work clogs.

In the late 20th century, the sort of leather-upper clogs that had long been popular in Scandinavian countries became fashionable, particularly for women, usually in an open-back style (such clogs are also, technically, mules), or a slingback style; in the early 21st century, a closed-back version also became popular with both men and women. Women's fashion sandals with traditional clog soles have also become popular in recent years.

Klompen are still worn by a small number of older farmers and fishermen in The Netherlands. In the past, many groups of people in the Netherlands would wear klompen as their everyday shoes. These clogs are made (mostly) of willow-wood and provide a warm, insulated and safe form of footgear. Traditionally, a farmer's klompen have rounded toes, while a fisherman's have pointed toes (like those of the ornamental klompen made for the tourist trade), to assist in stretching nets. Mostly, klompen have been replaced by rubber boots.

Clogs are still used today, both in gardens and road-work, but also for decoration, such as those intended for tourists for use as flowerpots or wall ornaments. Traditional Scandinavian-style clogs, particularly when made of either rubber or plastic instead of wood, are also frequently worn by chefs, doctors, nurses, and others whose work requires long hours of standing, because of the support a well-made pair provides (and, in the case of all-plastic versions, because they are easy to clean, with some heat-resistant plastic hospital clogs even being autoclave-safe); in such cases, however, more cheaply-made versions that are neither padded nor contoured, and thus have little or no support, are not generally regarded as useful. Clogs were tested for compliance to European safety standards and found to meet those standards.

Standard klompen cost about €10 for a size 10. Painted in yellow or black (traditional colors) this may be upto €12. When purchased in tourist areas prices range up to €20 or even €30 a pair. Well-made Scandinavian-style clogs, suitable for use as work shoes, tend to be quite expensive, but also both comfortable and durable.