In order of decreasing wavelength:
Radio Waves
Microwaves
Infrared light
Red light
Violet light
Ultraviolet light
X-rays
Gamma rays
Explanation:
The electromagnetic spectrum is a classification of all the electromagnetic waves depending on their wavelength and their frequency. The waves with longest wavelength are radio waves, which have wavelenght that spans from a few mm up to several km. The waves with shortes wavelength are gamma rays, which have wavelength shorter than 10 picometers.
More or less at the centre of the electromagnetic spectrum light the visible part of the spectrum, which is usually classified into 7 colors: red, orange, yellow, green, blue, indigo and violet (decreasing wavelength). Red light is the color with longer wavelenght (approx. 750 nanometers), while violet light has the shortest wavelength (approx. 380 nanometers).