This Book systematically explores the formation and development of the mass line thought of the Chinese Communist Party, and analyzes its mass viewpoint under different historical conditions, including: (1) Formation and theoretical generalization of the mass line thought. For the first time, the Communist Party of China realized the transformation of the revolutionary subject from the elite to the masses. (2) Continuations and setbacks of the mass line thought. After the founding of the People's Republic of China, the general implementation of democratic centralism in national institutions and organizations, and the establishment of political consultation system and the system of people's congress fully reflect the application of the Party's mass line in the establishment of specific systems. (3) Restoration and innovation of the mass line thought. Since the Reform and Opening-up, the Party has restored the fine tradition of the mass line. DENG Xiaoping's theory of "People's Support", "People's Approval", "People's Delightfulness" and "People's Agreement", JIANG Zemin's "Three Represents", and HU Jintao's theory that "The government must function by the mandate of the people, empathize with the feelings of the people, and work for the well-being of the people" all reflect the innovation of the Party's mass line in the new century."