In architecture, the core is a vertical space used for circulation and services. It can also be called circulation core or service core. A core may contain stairs, elevators, electrical wiring, and pipes.

The core allows people to move between floors of a building and distributes services efficiently to each floor. The core can also play a key structural role in a building, helping to support it and acting as a load-bearing element with load-bearing walls.[1]​[2]​.

Office building cores tend to be larger than apartment building cores because office buildings have to handle more traffic with a greater number of elevators.[3]​ In general, it is desirable for the core to be as small as possible to maximize the usable floor area of ​​the building.[4]​.

The core is usually located in the center of the building, but it can also be placed at one end of the building and there can be multiple cores in a building. The cores that are located on one side of the building are known as perimeter cores, they are completely inside the building and can allow the interior space to be more open and have fewer pillars. The exterior cores are similar to the perimeter cores, but are located totally or partially outside the building. Nuclei divided into several smaller nuclei are called mixed nuclei. A large proportion (more than 40%) of skyscrapers with exterior cores were built after 2010. This type of core can also be used for the purpose of providing shade from the sun.[5]​[6]​.