A subnotebook (also called an ultraportable or mini notebook) is a class of laptop computers that are smaller and lighter than a typical laptop.

These computers are often confused with the "ultra-mobile PC" category, which is the name of a platform of small form-factor tablet PCs. Unlike UMPCs, they generally are found to run full desktop operating systems such as Windows or Linux, rather than specialized software such as Windows CE, Palm OS or Internet Tablet OS. They are also sometimes confused with netbooks which are a different category of devices that branched off from mini notebooks in general with the coming of the first of such devices, the EEE PC. Netbooks are most often much less expensive than Subnotebooks, as they are optimized for use as portable Internet capable devices and generally lack the processing power of a workstation. Netbooks typically have 9W TDP CPUs, sacrificing performance for power efficiency, whereas subnotebooks often use 18W TDP processors.

Subnotebooks are smaller than full sized laptops but larger than handheld computers. They often have smaller-sized screens, less than 14 inches, and weigh less than typical laptops, usually being less than 2 kg (4.4 lbs). The savings in size and weight are usually achieved partly by omitting ports or having removable media or optical disc drives. Many can be paired with docking stations to compensate.