A USB hub is a device that allows many USB devices to be connected to a single usb port hub on a host computer or another hub.

Wireless usb hub are often built into equipment, such as keyboards, monitors, printers, or computers. When a computer has several USB ports they might all be part of one internal USB hub rather than each port having independent USB hardware.

Physically separate USB hubs come in a wide variety of form factors: from boxes (looking similar to a network hub as shown above) connectible with a long cable, to small designs that can be directly plugged into a USB port (see the 'compact design' picture). In the middle case, there are "short cable" hubs which typically use an integral 6 inch cable to slightly distance a small hub away from physical port congestion and of course increase the number of available ports.

Also available are so-called "sharing hubs", which effectively are the reverse of a USB hub, allowing several PCs to access (usually) a single peripheral. They can either be manual, effectively a simple switch-box, or automatic, incorporating a mechanism that recognises which PC wishes to use the peripheral and switches accordingly. They cannot grant both PCs access at once. Some models, however, have the ability to control multiple peripherals separately (e.g. 2 PCs and 4 peripherals, assigning access separately). Only the simpler switches tend to be automatic, and this feature generally places them at a higher price point too.

A USB network with many devices requires one or more hubs connected to each other. USB hubs can extend a USB network a maximum of five times. The USB specification requires that bus-powered hubs may not be connected in series to other bus-powered hubs.

USB ports are often closely spaced, so that plugging a device into one port may physically block an adjacent port, particularly when the plug is not part of a cable but is integral to a device such as a USB flash drive. A horizontal array of horizontal sockets, may be easy to fabricate, but can sometimes cause say only two out of four ports to be usable (depending on plug width).

Port arrays in which the port orientation is perpendicular to the array orientation generally have fewer blockage problems. 'Octopus' hubs (with each socket at the end of a very short cable), or 'star' hubs (with each port pointing in a different direction, as pictured) avoid this problem completely.

Aside from practical layouts, novelty USB hubs have also been produced, such as one shaped like the TARDIS, a fictional time-travelling space ship from the BBC science fiction series Doctor Who, or another shaped like a nuclear missile launch console complete with a big red button (which shuts down the PC).

Laptop computers may come with many USB ports built in, but an external USB hub can consolidate several everyday devices (like a mouse and a printer) into a single port for quick attachment and removal.