The Bucharest Nine or the Bucharest Format is an organization founded on 4 November 2015 in Bucharest, Romania, at the initiative of the President of Romania Klaus Iohannis and the President of Poland Andrzej Duda during a bilateral meeting between them. Its members are Bulgaria, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Romania and Slovakia. Its appearance was mainly a result of a perceived aggressive attitude from Russia following the annexation of Crimea from Ukraine and its posterior intervention in eastern Ukraine both in 2014. All members of the B9 were either part of the former Soviet Union (USSR) or members of the defunct Soviet-led Warsaw Pact.

Klaus Werner Iohannis, sometimes referred to by his initials KWI in the Romanian press, is a Romanian politician, physicist, and former physics teacher who has served as president of Romania since 2014. He became the president of the National Liberal Party (PNL) in 2014, after previously serving as the leader of the Democratic Forum of Germans in Romania (FDGR/DFDR) between 2002 and 2013. Prior to entering national politics, he was a physics teacher at the Samuel von Brukenthal National College in his native Sibiu.