Peter Waage (29 June 1833 – 13 January 1900) was a Norwegian chemist and professor of chemistry at the University of Kristiania.

Along with his brother-in-law Cato Maximilian Guldberg, he co-discovered and developed the law of mass action between 1864 and 1879.

He was the son of Peder Pedersen Waage (1796–1872) and Regine Lovise Wathne (1802–72).

In 1858, he received the Crown Prince's gold medal (Kronprinsens gullmedalje) for work on the development of a theory of oxygen-containing acid radicals.

He subsequently traveled to France and Germany, where he studied for two years including time spent with Robert Bunsen in Heidelberg.