How would you recognize a mode of participation if you see one? Owing to the rapid expansion of political activities in the last decades this question has become increasingly difficult to answer. Neither the development of all-embracing nominal definitions, nor deductive analyses of existing modes of participation seem to be helpful. In addition, the spread of expressive modes of participation makes it hard to avoid purely subjective definitions. The aim of this discussion paper is to develop an operational definition of political participation, which allows us to cover distinct conceptualizations systematically, efficiently and consistently. This goal can only be arrived at if the conventional approach of presenting nominal definitions to solve conceptual problems is left behind. Instead, available definitions are included in a set of decision rules to distinguish three main variants of political participation. A fourth variant is distinguished for non-political activities used for political purposes. Together, the four variants of political participation cover the whole range of political participation systematically without excluding any mode of political participation unknown yet. At the same time, the endless expansion of the modes of political participation in modern democracies does not result in an endless conceptual expansion. Implications for research and various examples are discussed.