This chapter focuses on the presence, characteristics and uses of pendulum clocks at the Royal Observatory of Paris in the early eighteenth century. Through the analysis of unpublished manuscripts, I argue that such clocks were crucial to the organisation of work at the Observatory and to the performance of common astronomical observations. I also consider the European circulation of knowledge about these clocks, as evidenced by exchanges of letters and other publications. In fact, the study of the history of the Observatory’s pendulum clocks makes it possible to illustrate the concrete functioning of the institution, its place in the European scene, as well as the ambitious cultural-political projects behind its activities.