无线电（意大利语、德语、英语、法语、西班牙语: Radio），又称无线电波、射频电波、电波，或射频，是指在自由空间（包括空气和真空）传播的电磁波，在电磁波谱上，其波长长于红外线光（IR）。频率范围为300 GHz以下 ，其对应的波长范围为1公尺以上。就像其他电磁波一样，无线电波以光速前进。经由闪电或天文物体，可以产生自然的无线电波。由人工产生的无线电波，被应用在无线通信、广播、雷达、通信卫星、导航系统、电脑网络等应用上。

无线电发射机，借由交流电，经过振荡器，变成高频率交流电，产生电磁场，而经由电磁场可产生无线电波。无线电波像磁铁，有同性相斥、异性相吸的现象。同类电子会互相排斥，因此当无线电波射出时，会将前方电波往前推，当连续电波一直射出来时，电波就会在空气中传播。

Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies from 3 THz to as low as 3 kHz, and corresponding wavelengths ranging from 100 micrometers (0.0039 in) to 100 kilometers (62 mi). Like all other electromagnetic waves, they travel at the speed of light. Naturally occurring radio waves are made by lightning, or by astronomical objects. Artificially generated radio waves are used for fixed and mobile radio communication, broadcasting, radar and other navigation systems, communications satellites, computer networks and innumerable other applications. Radio waves are generated by radio transmitters and received by radio receivers. Different frequencies of radio waves have different propagation characteristics in the Earth's atmosphere; long waves can diffract around obstacles like mountains and follow the contour of the earth (ground waves), shorter waves can reflect off the ionosphere and return to earth beyond the horizon (skywaves), while much shorter wavelengths bend or diffract very little and travel on a line of sight, so their propagation distances are limited to the visual horizon.