Until the 1970s, when superconducting magnets became common, iron-cored electromagnets were normally used to produce steady magnetic fields of high intensity. We will follow the evolution of laboratory electromagnets, used to investigate the magnetic, magneto-optical or atomic properties of materials, from Michael Faraday to Pierre Weiss and his followers. Other forgotten models of electromagnets (du Bois, ...) will be mentioned. This evolution culminated with the construction of the large Leiden electromagnet and the giant ones at Meudon-Bellevue (near Paris) and Uppsala. This paper will focus on the electromagnets designed by the French physicist Pierre Weiss (1865-1940), who made pioneering studies of ferromagnetic materials, giving his name to the uniformly magnetized “Weiss domains”. From 1895 to 1899, he was “Maître de Conférences” at the University of Rennes (France). While in Rennes, he published in 1898 an article describing an electromagnet based on the novel rectangular-framed geometry already used by Rühmkorff in 1849, with two coaxial cylindrical coils around the poles. Following an idea by Ewing, he added a third coil around the yoke. A prototype has been rediscovered in the collections of scientific instruments at the University of Rennes 1. Later on, this type of magnet was available from several makers. One of them is exhibited in Florence. In 1902, Weiss became professor and director of the Physics Laboratory at the ETH in Zurich. In 1907, he published the design of the first truly modern electromagnet. The electromagnet, built by Maschinenfabrik Oerlikon and installed at ETH-Zurich, has been lost. An improved one, dated 1914, made for Jean Becquerel at the Muséum (Paris), can still be seen at Meudon. The largest one following this pattern (14 t) was installed in Leiden around 1930 and is now exhibited at the Boerhaave Museum. In 1918, after the return of Alsace to France, Pierre Weiss went to the University of Strasbourg where he founded and directed for 20 years a laboratory dedicated to magnetism studies. He worked with the French physicist Aimé Cotton on the project of the giant electromagnet (120 t) of Bellevue. A whole range of laboratory electromagnets, following the pattern proposed in 1907, and including improvements especially in the cooling system, were built by well-known manufacturers: Maschinenfabrik Oerlikon-Zurich, SIP-Genève, Siemens & Halske, Carpentier, Ducretet, etc. Small ones are still in production now.