The electromagnetic spectrum (often just called the spectrum) is the range of all frequencies of electromagnetic radiation. In theory the frequencies range from 0 Hertz to infinite Hertz.  Frequencies of 0 Hertz can exist, but the lowest non-zero signal known is the 22 year sun spot cycle which has a period of 22 years, or a frequency of 1.4*10^-9 Hz. At the other extreme, the highest frequency measured is a 10²⁴ Hz photon generated by colliding electrons with positrons of sufficient energy. In theory, photons of any arbitrarily high frequency could be created, but we are limited by the particle smashing technology that we currently have.

While the electromagnetic spectrum is simply a physical property of the world we live in, the use of bands in the electromagnetic spectrum is regulated by the government in most countries. The process of regulating and managing the use of the electromagnetic spectrum is called frequency allocation, or spectrum allocation. Generally, international bodies help guide the national bodies on how to manage frequency allocations because electromagnetic spectrum do not stop at national boundaries. A number of forums and standards bodies work on standards for frequency allocation, including:

• ITU – International Telecommunications Union
• CEPT – European Conference of Postal and Telecommunications Adminstrations
• ETSI –
• CISPR – International Special Committee on Radio Interference
• In Canada, the spectrum is managed by Innovation, Science and Economic Development Canada

The chart below shows the radio spectrum allocations in Canada.