Hot swapping is the replacement or addition of components to a computer system without stopping, shutting down, or rebooting the system. Hot plugging describes only the addition of components to a running computer system. Components which have such functionality are said to be hot-swappable or hot-pluggable; likewise, components which do not are cold-swappable or cold-pluggable. Although the broader concept of hot swapping can apply to electrical or mechanical systems, it is usually mentioned in the context of computer systems.

An example of hot swapping is the express ability to pull a Universal Serial Bus (USB) peripheral device, such as a thumb drive, mouse, keyboard, or printer out of a computer's USB slot without powering down the computer first.

Most desktop computer hardware, such as CPUs and memory, are only cold-pluggable. However, it is common for mid to high-end servers and mainframes to feature hot-swappable capability for hardware components, such as CPU, memory, PCIe, SATA and SAS drives.

Most smartphones and tablets with tray-loading holders can interchange SIM cards without powering down the system.

Dedicated digital cameras and camcorders usually have readily accessible memory card and battery compartments for quick changing with only minimal interruption of operation. Batteries can be cycled through by recharging reserve batteries externally while unused. Many cameras and camcorders feature an internal memory to allow capturing when no memory card is inserted.

Hot swapping is primarily used whenever it is desirable to change the configuration or repair a working system without interrupting its operation. A typical example of needing to keep a system running at all times is in the case of a server, a computer that provides access to essential data and applications needed by other computers called clients. At other times, hot swapping is implemented simply to avoid the delay and nuisance of shutting down and then restarting a device, such as in the case of charging a smartphone.

Hot swapping is used to add or remove peripherals or components and to replace faulty modules without interrupting equipment operation. For example, a machine may have dual hot-swappable power supplies, each adequate enough to power the machine on its own. If one of those power supplies breaks and shuts down, the machine will not shut down, as it will draw power from the other, functional power supply. The faulty power supply can be replaced during operation of the machine, eventually bringing the machine back to a state of redundancy. In the context of servers, important expansion cards, such as disk controllers or host adapters, may be designed with specialized redundancy features in order for these to be replaceable without necessitating interruption of server operation.

Another use case of hot swapping is to enable faster data synchronization between two devices by not having to power down either device before connecting them together. For example, plugging an iPhone to a Mac computer via a USB cable to synchronize data between them does not require powering down either the iPhone or the Mac and waiting for them to restart. For even more convenience, data synchronization can be configured to start automatically without user input. It is also possible to interrupt the data synchronization at any time simply through unplugging the devices, although it's not recommended to do so until instructed to avoid data corruption.