Paul Niggli (26 June 1888 – 13 January 1953) was a Swiss crystallographer, mineralogist, and petrologist who was a leader in the field of X-ray crystallography.

Niggli was born in Zofingen and studied at the Swiss Federal Institute of Technology (ETH) in Zürich and the University of Zurich, where he obtained a doctorate.

[2] In 1920, Niggli became the lead scientist at the ETH's Institut für Mineralogie und Petrographie, where he brought his systematic approach to the study of crystal morphologies using X-ray diffraction.

In 1935, Niggli and his doctoral student Werner Nowacki (1909–1988) determined the 73 three-dimensional arithmetic crystal classes (symmorphic space groups).

Since 1988 the Paul Niggli Foundation awards medals to outstanding Swiss mineral scientists below the age of 35 with a strong perspective for an academic career.