A Network interface card (also known as a NIC, network card, or network interface controller) is an electronic device that connects a computer to a computer network, usually a LAN. It is considered a piece of computer hardware. Most modern computers support an internal network interface controller embedded in the motherboard directly rather than provided as an external component.

Network cards let a computer exchange data with a network. To achieve the connection, network cards use a suitable protocol, for example CSMA/CD. Network cards usually implement the first two layers of the OSI model, that is the physical layer, and the data link layer. There are older network protocols such as ARCNET, introduced in 1977, LocalTalk or Token Ring, but today, most network cards use Ethernet.

A network card, as it was common in the 1990s. This card was used for ethernet. It has both a 10Base2 connector for a coaxial cable and a 10BaseT connector for a twisted pair cable

Ethernet cards are available in several different standard packages called form factors that have evolved over the last several generations of PC hardware:

• In the 1990s and early 2000s, large Industry Standard Architecture cards were the first standard for PCs. Computer owners had to open the computer's case to install the card.
• Newer Ethernet cards installed inside desktop computers use the Peripheral Component Interconnect standard and are usually installed by the manufacturer. These cards are still common in desktop PCs, for computers whose motherboards do not contain an onboard Ethernet port.
• Smaller Personal Computer Memory Card International Association Ethernet cards that resemble credit cards are readily available for laptop and other mobile computers. These insert conveniently into slots on the side or front of the device. The PC Card is a common PCMCIA device, although only certain PC Card and PCMCIA products support Ethernet. By the early 2010s, however, fewer laptops supported the PCMCIA standard.
• Though they look more like small boxes than cards, external USB Ethernet adapters also fill a market niche. These devices are a convenient alternative to PCI cards for desktop computers and they're also commonly used with video game consoles and other consumer devices lacking PCMCIA slots and devices.