Since the beginning of the Reform and Opening, social organizations () have proliferated rapidly, promoting, in the process, individual participation, allowing individuals to create social value, and expanding the social sphere. Social organizations are thus playing an increasingly rich social role, and have undeniably become a part of China’s social transition. At the same time, increases in the breadth and depth of social organizations are facilitating their integration into the mainstream of social progress, and helping them to become, in complement to state and market systems, a new civil society system. Analyzing the 30-year rise of social organizations as well as trends in their development from the angles of growth in number, social participation, organizational structures, and fields of activity, we can see that the appearance and growth of social organizations is a necessary result of the Reform and Opening, and of China’s social transition. After 30 years of practice, a relatively rich, diverse, and open ecosystem of associations has gradually formed. As the most populous form in the ecosystem, social organizations are becoming increasingly normalized and orderly; the scope of their activities, too, is broadening. In today’s China, economic development, social harmony, and political civilization are all increasingly inseparable from social organizations.