1) What is the definition the political parties? W. Phillips Shively defines political parties as: A political party is a group of officials or would be officials who are linked with a sizable group of citizens into an organization; a chief object of this organization is to ensure that its officials attain power or are maintained in power.  Actually, political party is a group of people with similar opinions and aims, who act as one unit, express one ideology and everybody from the party have to share it. Also, political party act as a link between government and society (citizens) through some institutions and directly by communication with people to represent interests of each other's. It's important to mention, that without interconnection of these two sides, it's impossible to govern the state. Moreover, different political parties have different ideology, it's so called "party families  for example: The Social Democrats, which is the most powerful, The Communists, The New Life, Green Parties, The Christian Democrats and etc. 2) What are the main functions of the political parties? One of the main purpose of the political parties is uniting people in one group and nominate to an office the leader of the political party, who will represents their interests, goals and mainly could take a power. Second one is a policy making process, basically, political parties take positions on important policy questions and when political party have enough power, they may put the idea on examination through legislation. If the majority will approve this activity, consequently, the candidate take a mandate to carry out the program. I have to add that, coalition (majority of members) which consist from political parties represent the Government and there is an opposition side (minority of members), moreover, they always want to be instead of majority to run the state. 3) Who are the main political scientists' works on political parties? How did they classify the political parties? There are a large number of scientists, who are studying political parties, but the greatest two are W. Phillips Shivley and Maurice Duverger. Actually, they have their own points of view. Phillips Shivle