Public sector seed programs in most sub-Saharan African countries targeted the dissemination of quality seed of improved varieties in the 1970 and '80s, assuming that the informal seed system would disappear. The orientation in 1990s shifted toward withdrawal of the public sector, promoting privatization and liberalization of the seed market. The informal seed system remained dominant. Integrated seed sector development aims to better link informal and formal seed systems, and balance public and private sector involvement. It explores variation among seed value chains, with the aim of making seed programs and policies more coherent with farmers' practices and more effective at reaching food security.