Deoxyribonucleosides or ribonucleosides are collectively called nucleosides. A nucleoside differs from a nucleotide in lacking a phosphate. Nucleosides are named according to the base they contain.

Nucleosides are composed of a base (adenine, guanine, cytosine, thymine, or uracil) attached to a sugar (ribose for ribonucleosides or deoxyribose for deoxyribonucleosides).

Corresponding to the bases above, common ribonucleosides are named adenosine, guanosine, cytidine, and uridine, respectively. Common deoxyribonucleosides are named deoxyadenosine, deoxyguanosine, deoxycytidine, deoxyuridine, and (deoxy)thymidine, respectively.