1-Wire is a device communications bus system designed by Dallas Semiconductor that provides low-speed (16.3 kbit/s) data, signaling, and power over a single conductor.

1-Wire is similar in concept to I²C, but with lower data rates and longer range. It is typically used to communicate with small inexpensive devices such as digital thermometers and weather instruments. A network of 1-Wire devices with an associated master device is called a MicroLAN. The protocol is also used in small electronic keys known as a Dallas key or iButton.

One distinctive feature of the bus is the possibility of using only two wires — data and ground. To accomplish this, 1-Wire devices include an 800 pF capacitor to store charge and power the device during periods when the data line is active.