In each type of political institution, advocacy groups will vary and the degree of influence of this relationship on the country's policy making, political system and democracy will also vary. Within the interest group in general, there are legitimate, legal and positive interest groups, promoting the development of society. On the contrary, there are unwarranted, illegal benefits, hindering development. The book gathers the treatises of author Phan Duy Anh published in specialized journals, divided into two parts: Part 1: The relationship between political parties and advocacy groups in modern Western democracies; Part 2: Political party and advocacy group in modern American democracy.