Environmental regulations and the competitiveness of pulp production are very often in conflict with each other. Thanks to its capability to partly or totally replace chlorine-based chemicals, ozone bleaching offers a unique opportunity to meet both these constraints. Reduction of fresh water usage and limitation in effluent rejects are already “external” driving forces for long-term sustainability in pulp production. Ozone has proven to be one of the best candidates to reduce AOX, COD emission and fresh water usage.