Ostwald may refer to:
- Friedrich Wilhelm Ostwald, the physico-chemist (Nobel Prize of Chemistry, 1909)
- The Ostwald's rule related to the polymorphism: the least stable phase is first formed
- The Ostwald Process, a synthesis method for making nitric acid from ammonia
- Ostwald ripening, a crystallization effect
- Ostwald, Bas-Rhin, a commune of the Bas-Rhin département, in France