The Ae 6/6 is a heavy electric locomotive used by the SBB-CFF-FFS. It is sometimes also referred to as canton locomotive ("Kantonslokomotive"), because the first 25 locomotives were named after the cantons, and carried the canton's coat of arms on the side. Other 95 locomotives received names of capital cities of Swiss cantons, or names of other towns and cities. The naming was held as a ceremony in the respective cities.

Originally designed for heavy services on the Gotthard route, as many Swiss locomotives were, the Ae 6/6 was one of the classic Gotthard locomotives. The specification, created in 1949, included that the locomotive to be developed must be able the pull a 600 tonne train over the 26‰ gradients of the Gotthard line at 75 km/h. The first prototype with the number 11401 was scheduled for delivery in 1952. Intense trial runs were made with the prototypes. They had bogies with fixed axles, which led to heavy rail and wheel flange abrasion. Despite some early technical issues, the SBB-CFF-FFS were convinced they were on the right path with the development of the Ae 6/6. After introducing side-elastic wheelsets and making the wheel flanges of the middle axles smaller, the series production started in 1954, resulting in the first series locomotives delivered in 1955.

In its heyday, the 1950s and 1960s, the Ae 6/6 was the Gotthard locomotive par excellence, both for passenger and freight traffic. They were also used on the route through the Simplon tunnel. They were used in turns to ensure regular servicing in the main maintenance facility at Bellinzona. In the late 1960s, the two prototypes were retired from service on the Gotthard line; gradually followed by the rest of the class. After the introduction of the Re 6/6 locomotives, most Ae 6/6 were reallocated to services in the Swiss plateau. Since this time, they have been mostly used for freight trains, because they are too slow for the faster passenger services. An exception were those units hired by the BLS, which were sometimes used to haul relief and intercity trains over the Lötschberg route.

In 1999, all 120 locomotives were assigned to the SBB-CFF-FFS cargo division (SBB Cargo) following the internal reorganisation of the SBB-CFF-FFS. Due the fact that the Ae 6/6 have three-axle bogies, they are deemed "rail killers" because of the higher rail abrasion compared to engines with two-axle bogies. This was especially considered an issue for freight runs on the Porrentruy-Bonfol route.

One of the biggest disadvantages of the Ae 6/6 is said to be the lack of multiple unit train control, which makes operating two engines together impractical. At one time, retrofitting this feature was proposed, but these plans were discarded due to the uncertain future of the locomotive. It was also considered to equip some of the newer engines with cab signalling, to allow them to run on cab signalling only-routes. This was tentatively done on the 11512 «Horgen».

The remaining operational locomotives were used for freight trains, but often they were just standing about in larger shunting yards. After the coats of arms were found to be stolen repeatedly (mostly as a souvenir, because it is generally assumed that the Ae 6/6 won't stay in service much longer and will eventually be scrapped), SBB Cargo ordered their removal in March 2005 and presumably turned them over to SBB Historic.

In 2009 SBB-CFF-FFS announced that 65 of the class will be withdrawn from service because of the slump in demand caused by the recession. The units will be stored pending an upturn whilst 12 will probably be scrapped or cannibalised.

Today they are around 14 SBB Ae 6/6's in preservation owned by SBB Historic or other organizations.

All locomotives were originally painted in the SBB CFF FFS green livery, with the number, and either SBB CFF, or SBB FFS on each side. In recent times about half were painted red, and a proportion of the fleet have been repainted in SBB Cargo livery, with all raised chrome embellishments removed apart from the Swiss coat of arms on each end. These locomotives have been renumbered (as class 610) in line with the current Swiss numbering scheme.