NCO may refer to:
- NCO Group, an international corporation that provides customer service contracting
- Net Capital Outflow, an economic metric measuring the amount of money from a country holding assets elsewhere
- NetCDF Operators, a suite of programs for manipulating NetCDF files
- National Children's Orchestra, an organisation for young musicians in the United Kingdom
- Network-centric operations, an emerging theory of war in the information age
- Non-commissioned officer in the rank structure of many armed forces worldwide
- Numerically controlled oscillator, a digital signal generator
- Nuova Camorra Organizzata, a defunct Italian Camorra criminal organization in Naples founded by Raffaele Cutolo
- Isocyanate, a functional group of atoms –N=C=O