The International telecommunications Union, ITU frequency bands define a set of portions of the radio frequency spectrum: VLF, LF, HF, VHF, UHF, EHF, etc .
Recent Standardization Activities in ITU-R SG 3
ITU Archives - Microwave Link
What is RF? A radio frequency spectrum guide
High frequency - Wikipedia
Spectrum management: Key applications and regulatory considerations driving the future use of spectrum
Spectrum allocation, The IT Law Wiki
OFCOM Archives - Microwave Link
Confused about RF-band letter designations? That's not surprising!
ITU EMF Guide
ISM Bands Around the World, Blog