The Stadler KISS is a family of bilevel electric multiple unit commuter trains developed and built since 2008 by Stadler Rail of Switzerland. As of 2016, 242 KISS trainsets comprising 1,145 cars have been sold to operators in eleven countries. Boarding is done into the lower deck.

In the early stages of its development, the KISS was known as the Stadler DOSTO. This name was derived from the German word Doppelstock, meaning "double decker". This is still the name used for the Swedish market because "kiss" means "pee" in Swedish.

Since September 2010, Stadler refers to the train as "KISS", an acronym for "Komfortabler Innovativer Spurtstarker S-Bahn-Zug", meaning "comfortable, innovative, sprint-capable suburban train".

In Swiss Federal Railways (SBB) service, the train is classified as RABe 511, while a newer version for regional services is classified as RABe 512. BLS classifies them as RABe 515. For the Eastern European market (specifically in Russia, Georgia and Azerbaijan), it is branded Eurasia.

A total of 93 RABe 511 [de] trainsets (69 six-car/24 four-car units) were delivered to Swiss Federal Railways, numbered 511 001–511 093, some for use on the long-distance IR or RE lines (red-white-grey livery) and others on the Zurich S-Bahn network (red-white-blue livery) in the Zurich metropolitan area.

In Switzerland, it is common practice to name electric multiple units (e.g. SBB RABe 501, RABDe 500, RABe 514, SOB RABe 526, BLS RABe 515) and locomotives (e.g. SBB Ae 6/6, Re 6/6, Re 450, Re 460). Fourteen RABe 511 trainsets are named, mostly after Swiss communes or cantons with the name and respective coat of arms (COA) indicated at both ends of the trainset. The table below lists all named RABe 511 with their respective number (№). Trainsets of Zurich S-Bahn are indicated with an *:

The KISS family was created as the third generation of vehicles for the Zürich S-Bahn. Compared to previous generations, they are characterized mainly by a higher number of standing passengers per car, in part because the longer trains have proportionately fewer seats. The trains are 15 cm (5.9 in) wider due to placing the HVAC channels under the ceiling instead of behind side panels. The headroom is still two meters, because friction stir welded floor panels made from aluminium extrusions are used. The number of seats, however, is slightly lower than in the previous models. Like in the KISS's predecessors, low-floor entrances, vehicle air conditioning and vacuum toilets (two, including one wheelchair accessible) are available. There are also two multi-functional areas with storage space for strollers, bicycles and the like.

The six-car train set consists of two head power cars and four intermediate trailers. In the power heads, all axles are powered. The "Eurasia" version for the Russian gauge railways, in a six and four-car formation, has two trailer heads and two shorter intermediate power cars, and also two intermediate trailers in a six car formation. A special diesel-electric version of the "Eurasia" train, which first appeared in 2021, is manufactured in an eight-car formation, including 2 double-deck head cars, 2 diesel generator cars, 3 intermediate double-deck cars and 1 single-deck car.