Paul Niggli (June 26, 1888 – January 13, 1953) was a Swiss crystallographer 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 Zurich and the University of Zurich, where he obtained a doctorate. His 1919 book, Geometrische Kristallographie des Diskontinuums, played a seminal role in the refinement of space group theory.