Haldor Topsøe is a Danish catalysis company founded in 1940 by Haldor Topsøe (1913–2013).

Haldor Topsøe specialises in the production of heterogeneous catalysts and the design of process plants based on catalytic processes. Focus areas include the fertiliser industry, chemical and petrochemical industries, and the energy sector (refineries and power plants).

Haldor Topsøe A/S is one of the world’s leading companies within the field of heterogeneous catalysis, and over 50 per cent of the ammonia used for fertilizer on a worldwide scale is made with the help of technology from Haldor Topsøe.