罗伯特·史都华，第二代伦敦德里侯爵，KG，GCH，PC（Robert Stewart, 2nd Marquess of Londonderry，1769年6月18日－1822年8月12日），盎格鲁-爱尔兰政治家，通称卡苏里子爵（Viscount Castlereagh），曾任外务大臣，于1814年至1815年代表英方出席维也纳会议，后来因工作过劳而精神失控，自杀身亡。

Robert Stewart, 2nd Marquess of Londonderry KGGCHPCPC (Ire) (18 June 1769 – 12 August 1822), usually known as Lord Castlereagh (/ˈkɑːsəlreɪ/ KAR-sul-RAY), was an Irish/British statesman. As British Foreign Secretary, from 1812 he was central to the management of the coalition that defeated Napoleon and was the principal British diplomat at the Congress of Vienna. Castlereagh was also leader of the British House of Commons in the Liverpool government from 1812 until his suicide in August 1822. Early in his career, as Chief Secretary for Ireland, he was involved in putting down the Irish Rebellion of 1798 and was instrumental in securing the passage of the Irish Act of Union of 1800.