A party system is a concept in comparative political science

Political science

Political Science is a social science discipline concerned with the study of the state, government and politics. Aristotle defined it as the study of the state. It deals extensively with the theory and practice of politics, and the analysis of political systems and political behavior...

 concerning the system of government by political parties

Political party

A political party is a political organization that typically seeks to influence government policy, usually by nominating their own candidates and trying to seat them in political office. Parties participate in electoral campaigns, educational outreach or protest actions...

 in a democratic country. The idea is that political parties have basic similarities: they control the government

Government

Government refers to the legislators, administrators, and arbitrators in the administrative bureaucracy who control a state at a given time, and to the system of government by which they are organized...

, have a stable base of mass popular support, and create internal mechanisms for controlling funding, information and nominations.

The concept was originated by European scholars studying the United States, especially James Bryce

James Bryce

James Bryce may refer to:*James Bryce, 1st Viscount Bryce , British jurist, historian and politician*James W. Bryce , American inventor and pioneer in magnetic data recording...

 and Moisey Ostrogorsky

Moisey Ostrogorsky

Moisey Ostrogorsky was a Belarusian political scientist, historian, jurist and sociologist. Alongside with Max Weber and Robert Michels, he is considered one of the founders of political sociology, especially in the field of theories about Party Systems and political parties...

, and has been expanded to cover other democracies.
Giovanni Sartori

Giovanni Sartori

Giovanni Sartori is an Italian political scientist specialized in the study of democracy and comparative politics.-Biography:Born in Florence in 1924. Sartori began his academic career as a lecturer in the History of Modern Philosophy...

 devised the most widely used classification method for party systems. He suggested that party systems should be classified by the number of relevant parties and the degree of fragmentation.