The Lagginhorn (4,010 m), also known as Laquinhorn or ts Lagg'ii, is a mountain in the Pennine Alps in Switzerland. It lies a few kilometres north of the slightly higher Weissmies and also close to the slightly lower Fletschhorn on the north.

The Lagginhorn is the last four-thousander in the main chain before the Simplon Pass; it is also the second-lowest four-thousander (number 58 of 60) in Switzerland. A rocky, mostly unglaciated summit, it is one of the few Alpine 4000m mountains accessible without any necessary glacier crossings and therefore can be climbed solo with appropriate experience.

The first ascent was by Edward Levi Ames and three other Englishmen, together with local Saas Grund clergyman Johann Josef Imseng, Franz Andenmatten (landlord of the Monte Rosa Hotel) and three other guides on 26 August 1856.

Lagginhorn's etymology is obscure but may derive from the Latin lacus or the Saracen arabic allâqîn. The local Saastal people call it ts Lagg'ii today.

The Lagginhorn and its neighbours within the Weissmies Range fall within the parautochthon of the Monte Rosa portion of the Middle Penninic Nappe.