Purpose -The purpose of this paper is to connect sociology, criminology, and social psychology to identify specific factors that keep protests peaceful, discusses empirical examples of effective peacekeeping, and develops practical peacekeeping guidelines. Design/methodology/approach -The analysis systematically compared 30 peaceful and violent protests in the USA and Germany to identify peaceful interaction routines and how they are disrupted. It employed a triangulation of visual and document data on each demonstration, analyzing over 1,000 documents in total. The paper relies on qualitative analysis based on the principles of process tracing. Findings -Results show that specific interaction sequences and emotional dynamics can break peaceful interaction routines and trigger violence. Single interactions do not break these routines, but certain combinations do. Police forces and protesters need to avoid these interaction dynamics to keep protests peaceful. Communication between both sides and good police management are especially important.Research limitations/implications -The paper highlights the need to examine the role of situational interactions and emotional dynamics for the emergence and avoidance of protest violence more closely. Practical implications -Findings have implications for police practice and training and for officers' and protesters' safety. Originality/value -Employing recent data and an interdisciplinary approach, the study systematically analyzes peacekeeping in protests, developing guidelines for protest organizers and police.Even demonstrations for peace can result in violence between protesters and police. Such violence has occupied media, the public, and various research fields for decades. Sociology, criminology, and social psychology have usually focussed on factors leading to violence. Scholars rarely ask what keeps protests peaceful to develop specific policy-oriented policing measures. Police studies call for applied research that contributes to improved policing and for research going beyond setting the organizational context as the main determinant of policing (Brodeur, 2005, p. 51 ff).This paper comparatively analyzes peaceful and violent demonstrations to determine empirically how and why demonstrations stay peaceful. Violence is defined here as a physical action with the intention of causing injury or death to another person. The paper asks three questions: Which factors ensure a peaceful protest? What do empirical cases look like in which peacekeeping is effective despite difficult circumstances? Which practical guidelines and measures can be derived from these cases to prevent protest violence?