NNL

NNL may refer to:
 * National Natural Landmark — a natural history conservation program of the U.S. Secretary of the Interior
 * National Nuclear Laboratory — the UK's government-owned commercially operated fully customer-funded nuclear technology service provider
 * Negro National League (1920–1931) — one of the several Negro leagues which were established during the period in the United States in which organized baseball was segregated
 * Negro National League (1933–1948) — established two years after the first Negro National League had disbanded
 * Noether normalization lemma — a theorem in commutative algebra
 * Narnaul railway station — a railway station in Haryana, India