The increase in number and visibility of non-state actors (NGOs, corporations, philanthropic foundations, social movements, think tanks, etc.) has shaken up the diplomatic game, forcing states to take them into consideration. They have also developed their own diplomatic activities, sometimes delegated by states, at other times in competition with or in opposition to them. What is the nature of these diplomatic activities? Are we witnessing an overhaul of diplomatic practices? Do they form a system such that one might refer to diplomacy by non-state actors? After analyzing the constitution and then the erosion of the regalian diplomatic monopoly, along with the history of non-state actors’ diplomatic involvement, this chapter will examine diplomatic activities that non-state actors have undertaken and practices they have revived, and then explore how governmental diplomacy has adapted, as well as the limits to forming a “diplomatic system” by non-state actors.