The development of European diplomacy has long been recognised as one of the main achievements of the early modern period. This story of diplomatic accord, however, often fails to take into account the fact that this was an uncertain time ravaged by warfare and upheaval, with states collapsing at an astonishing rate. How did diplomacy work amidst this volatile atmosphere? How did diplomats function when there were multiple semi-legitimate and legitimate forms of authority competing and co-existing? To answer these questions, Igor Pérez Tostado focuses for the first time on informal relations and ad hoc diplomatic channels, and on the shadowy agents, businessmen, assassins, martyrs and self-appointed diplomats that took the place of ambassadors and kings. Based on extensive archival research into hitherto unexplored sources across Europe, Anglo-Spanish Relations During the English Civil Wars offers a decisive and necessary new perspective on the development of both European diplomacy and politics in the 17th century. The wide-ranging and multi-disciplinary focus make this an important book for all scholars of European, British and Iberian history in the early modern period.