The Santos or Santos-Dumont is a wristwatch by Cartier. Considered to be the first men's wristwatch model, the first pilot's watch, and the first sports watch, it has changed dramatically over time but includes notable elements, including a screwed-on bezel with flat geometric shapes.

In 1904, Brazilian aviator Alberto Santos-Dumont was discussing the challenge of using a pocket watch while operating an airplane with his friend Louis Cartier. He directed his company to develop wrist-mounted watch, inspired by the novel ladies wristwatches of the time. Using a square pocket watch case, the resulting watch featured a large square dial with a screwed-on bezel and integrated lugs. Santos-Dumont wore such a watch when he was photographed flying his airplane in 1906, and it caused a sensation.

By 1911, Cartier was marketing “the Santos-Dumont watch” in platinum or gold, and the aviation connection made it a success with men who had not previously considered wearing wristwatches. The 25×35 mm rectangular watch used a movement supplied by Jaeger, and the two quickly established a lasting relationship and joint venture. The Santos is considered the first pilot's watch, but it was much more important than that, establishing wristwatches for men. Production of the initial square Santos-Dumont inspired models ended around World War II, as most countries specified round wristwatches for pilots.

Audemars Piguet shocked the world in 1972 with their revolutionary Royal Oak, which featured styling similar to the Santos-Dumont watch. The later Nautilus, also by designer Gerald Genta proved that high-end watch buyers would buy such a watch. Cartier redesigned the watch, re-launching the Santos de Cartier in 1978 with an integrated bracelet and stainless steel case. The two tone models of the 1980s were especially in demand, becoming one of the signature watches of the decade.

In 1987, Cartier re-designed the Santos line again, re-launching it as the Santos Galbée. It was more contoured than any previous model, with curved lugs and a slimmer body. The line was again refreshed in 2005 with an “XL” model added that measured 45×32 mm.

The Santos lineup was refreshed in 2018, with a new Cartier Santos Chronograph launched in 2019 at SIHH.