Purine (1) is a heterocyclic aromatic organic compound, consisting of a pyrimidine ring fused to an imidazole ring. Purines and pyrimidines make up the two groups of nitrogenous bases. These bases make up a crucial part of both deoxyribonucleotides and ribonucleotides, and the basis for the universal genetic code.

The general term purines also refers to substituted purines and their tautomers.

The purine is the most widely distributed nitrogen-containing heterocycle in nature.