第二代墨尔本子爵威廉·兰姆，PC，FRS（William Lamb, 2nd Viscount Melbourne，1779年3月15日 - 1848年11月24日），英国辉格党政治家，曾任内政大臣、首相。他曾热情辅导初登皇位的维多利亚。历史学家普遍对墨尔本评价不高，主要是因为他在任期间，既没有发生对外战争，也没有需要解决的国内问题，缺乏大成就、原则不明确。但是，主要研究18世纪的历史学家约翰·加农（John Cannon）称赞他“慈祥、诚实，又无私。”

William Lamb, 2nd Viscount Melbourne, PC,FRS (15 March 1779 – 24 November 1848), usually addressed as Lord Melbourne, was a British Whig statesman who served as Home Secretary (1830–1834) and Prime Minister (1834 and 1835–1841). He is best known for his intense and successful mentoring of Queen Victoria, at ages 18–21, in the ways of politics. Historians conclude that Melbourne does not rank high as a prime minister, for there were no great foreign wars or domestic issues to handle, he lacked major achievements, and he enunciated no grand principles. "But he was kind, honest, and not self-seeking." Melbourne was dismissed by the King in 1834, the last Prime Minister to have been dismissed by a Monarch.