Merck Serono (EMD Serono in the United States and Canada) is a pharmaceutical company headquartered in Darmstadt, Germany, and a brand and division of Merck focused on biopharmaceuticals.

In September 2006, Merck KGaA announced its intent to purchase the majority of Serono shares from Ernesto Bertarelli and the Bertarelli family. The Merck-Serono merger was announced on 21 September 2006. Merck KGaA and Serono operated as distinct entities until at least January 2007. As of January 5, 2007, Merck held the majority shares of Serono. The new company is called Merck Serono international SA. In 2012, Merck Serono moved its headquarters from Geneva, Switzerland to Darmstadt.

Drugs they market include Erbitux, UFT, Rebif, Novantrone, Gonal, Ovidrel/Ovitrelle, Zorbtive, Luveris, Saizen, Serostim, Glucophage, Concor and Euthyrox. Raptiva was withdrawn in 2007.

In the U.S. and Canada, Merck Serono is known as EMD Serono, as the former Merck subsidiary Merck & Co. holds the rights to the name Merck in those countries.