A laptop computer (also known as notebook computer) is a small mobile personal computer, usually weighing around from 1 to 3 kilograms (2 to 7 pounds). Notebooks smaller than an A4 sheet of paper and weighing around 1 kg are termed subnotebooks and those weighing around 5 kg a desknote (desktop/notebook). Predecessors of the laptop include the Osborne 1 and the Macintosh Portable, each of which weighed 20-30 pounds (9 to 14 kg) (due in part to being powered by hefty lead acid batteries) but nonetheless offered novel mobile computing platforms. Laptops are generally popular among students, travellers, and telecommuters. 

Laptops are capable of many of the same tasks that desktop computers perform, although they are typically less powerful. Laptops contain components that are similar to those in their desktop counterparts and perform the same functions but are miniaturized and optimized for mobile use and efficient power consumption. Laptops usually have LCD displays and smaller SODIMM (Small Outline DIMM) chips for their . In addition to a built-in keyboard, they may utilize a touchpad or a pointing stick for input, though an external mouse or keyboard can usually be attached.

Current models use LiIon batteries, which have largely replaced the older NiMH technology. Typical battery life for most laptops is two to five hours with light-duty use, but may drop to as little as one hour with intensive use. Batteries gradually degrade over time and eventually need to be replaced, commonly after two to five years.

Most modern laptops use an active matrix display, with screen sizes 14 inch (350 mm) or larger, and have PCMCIA expansion bays for expansion cards. Internal hard disks are smaller—2.5 inch (64 mm) compared to the standard desktop 3.5 inch (90 mm) drive—and have lower performance. Display adapters and sound cards are integrated. Modern laptops can often handle sophisticated games but tend to be limited by their fixed screen resolution and display adapter type. Docking stations are used for expanding connectors and quickly connecting many components to the laptop.

Laptops generally cost around twice as much as a desktop machine of similar specification. Performance is always lower than that of a comparable desktop because of the compromises necessary to keep weight and power consumption low. Upgradability is severely limited: typically only the RAM and hard drive can be changed. Because nearly all functions are integrated into the proprietary-design mainboard to save space and power, laptops are essentially non-repairable. Unless the unit is under warranty, the cost of repairing even a minor fault is close to the cost of simply buying a completely new laptop.