Until now, animal's natural behaviour and their interactions with humans were mostly studied by Biological Sciences. My research is in Human and Social Studies and aims at analysing the intersubjective work relationships between horses and humans. In this paper, I study work relationships between policemen and their patrol herses in urban environments, to show how each party invests in the joined realization of the work dedicated to enforcing law and order. The present study builds on a main theoretical framework: the Psychodynamics of work, which I use to analyse intersubjectivity of relationship between humans and animals in concrete work situations. The studies based on this theoretical framework already helped highlight the animals' subjective relationships to work and to confirm the existence of an 'animal working'. My study compares two research fields of work of police and horses. The results are expected to highlight the impacts of national or local contingencies, of the historicity of police units and of urban environments on life and the work relationship of policemen with their horses and horses with policemen. The first research field is situated within the French Republican Guard, which included some 460 horses. The Guard performs three missions: law and arder, military protocol of the state, and international prestige of France by promoting the French tradition of horse riding. For this study, I focus on their public safety missions. The second research field is situated within the municipal equestrian brigade of the French city of Tours. This is a rather small unit of six horses and six riders, which was created fifteen years ago. First, I will present the living and working conditions of horses in these two structures. Second, based on semi-structured interviews and observations of trainings and patrols, I will show how work is organized between humans and horses in both cases and how this organization impacts on the subjective commitment of horses in the work. Finally, I will attempt to determine whether work situations within same mission of public safety vary according to the national or local contingencies.