“International Humanitarian Law in Theory and Practice” is the first MOOC of the Kalshoven-Gieskes Forum on International Humanitarian Law, which is the platform within the Grotius Centre for International Legal Studies of Leiden University for the research, teaching and dissemination of international humanitarian law (IHL). In this course, Prof. Robert Heinsch, Dr. Giulia Pinzauti and Dr. Emma Irving will give you a deep insight into the rules that govern armed conflict, and aim to mitigate human suffering on the battlefield. You will explore the why and how of IHL, followed by the different types of conflict. In no time you will find out which rules apply to the civil war in Syria, the military intervention in Ukraine and the occupation of the West Bank. During this course, you will learn how hostilities should be waged: Which weapons can be used by combatants and other fighters? And, who should never be a target during military operations? We will also look into the concept of protected persons, and you will find out how IHL affords protection to the sick and wounded, medical personal, detainees, children, journalists and other persons who are not - or not anymore - fighting. At the end of this course, you are introduced to the different implementation and enforcement mechanisms that aim to increase respect for IHL. Here, you are invited to think critically whether IHL works!