The developing countries did not benefit from the economic growth of the developed countries. To remove this disparity, these 77 countries organised themselves into a group called the G-77 countries.
Later on, more developing countries joined the group and now it consists of about 130 countries. They have demanded a New International Economic Order, in which they have a real control over their natural resources, they get more development, assistance and fairer prices for raw materials exported by them. They want better access to the markets in developed countries for their manufactured goods. The Bretton Woods twins, IMF and World Bank were mainly set-up to favour the developed nations. They did not help the developing nations significantly as both of these institutions controlled their investments in the developing countries. So, the developing countries decided to set-up their own group, the G-77.