NK may refer to:
- Nagorno-Karabakh
- Natural killer cell
- Neturei Karta, a group of anti-zionist orthodox Jews
- New Kingdom
- North Korea
- Northrup-King Seed Company
- Nippon Kaiji Kyokai
- Nikšić, Montenegro license plates
- Nordiska Kompaniet, a department store in Stockholm, Sweden
- North Kesteven
- Spirit Airlines, which has IATA code NK
- Imerys, which has the Euronext ticker code NK
- Neue Kerze aka new candle, an old photometric unit of luminous intensity