Niels is a common Danish man's name, equivalent to Nicholas. The Norwegian and Swedish variant is Nils, and the pet form is Nisse. It may refer to:
In science:
- Niels Bohr, Danish physicist who made fundamental contributions to understanding atomic structure and quantum mechanics
- Niels Ferguson, Dutch cryptographic engineer and consultant who currently works for Microsoft
- Niels Ryberg Finsen, Faroese/Danish physician and scientist
- Niels Kaj Jerne, Danish immunologist
- Niels Krabbe, Danish ornithologist
In Danish music:
- Niels Viggo Bentzon, Danish composer and pianist
- Niels Wilhelm Gade, Danish composer, conductor, violinist, organist and teacher
- Niels-Henning Ørsted Pedersen, Danish jazz bassist known for his impressive technique
In politics:
- Niels Busk, Danish politician and Member of the European Parliament with the Venstre
- Niels Neergaard, Danish historian and political figure
- Niels Helveg Petersen, Danish politician
- Niels Treschow, Norwegian philosopher and politician
- Niels van den Berge, Dutch politician
In sports:
- Niels Feijen, Dutch three-time European straight pool champion
- Niels Holst-Sørensen, Danish European 400m champion
- Niels Christian Kaldau, Danish male badminton player
- Niels van Steenis, Dutch rower
- Niels van der Zwan, Dutch rower
In Danish royalty:
- Niels Ebbesen, Danish squire and national hero
- Niels of Denmark, king of Denmark following his brother Eric I
In Danish artistry:
- Niels Lauritz Høyen, the first Danish art historian and critic
- Niels Hansen Jacobsen, Danish sculptor and ceramist
In military:
- Niels Holst-Sørensen, commander-in-chief of the Royal Danish Air Force
- Niels Juel, Danish admiral
- Niels Jonsson Stromberg af Clastorp, Swedish soldier and Governor-General of Swedish Estonia from 1706 to 1709
In other fields:
- Niels Aagaard, professor at Sorø Academy
- Niels Henrik Abel, Norwegian mathematician
- Niels Hemmingsen (Nicolaus Hemmingius) 1513–1600, Danish theologian