Various forms of self-expression and protest are sometimes restricted by governmental policy (such as the requirement of protest permits), economic circumstances, religious orthodoxy, social structures, or media monopoly. One state reaction to protests is the use of riot police. Observers have noted an increased militarization of protest policing, with police deploying armored vehicles and snipers against the protesters. When such restrictions occur, protests may assume the form of open civil disobedience, more subtle forms of resistance against the restrictions, or may spill over into other areas such as culture and emigration.
A protest itself may at times be the subject of a counter-protest. In such a case, counter-protesters demonstrate their support for the person, policy, action, etc. that is the subject of the original protest. In some cases, these protesters can violently clash.
A protest can take many forms. The Dynamics of Collective Action project and the Global Nonviolent Action Database are two of the leading data collection efforts attempting to capture protest events. The Dynamics of Collective Action project considers the repertoire of protest tactics (and their definitions) to include:
The Global Nonviolent Action database uses Gene Sharp's classification of 198 methods of nonviolent action. There is considerable overlap with the Dynamics of Collective Action repertoire, although the GNA repertoire includes more specific tactics. Together, the two projects help define tactics available to protesters and document instances of their use.