As the HIV and AIDS epidemic unfolds, it increasingly poses complex development challenges for countries. Mainstreaming HIV and AIDS into national development processes remains a key approach to addressing both the direct and indirect causes of the growing epidemic. By ensuring the integration of planning, resource and programming issues, mainstreaming enables a multisectoral and multi-stakeholder response. The critical relationship between sector mainstreaming and mainstreaming in national development processes is represented. The close interdependence of the two processes usually involves interaction between the same national actors, planning authorities and development partners. Countries should undertake mainstreaming at the sectoral level as a way of establishing a multisectoral,  multi-level response that is also responsive to larger national development goals. However, the key is to understand sector mainstreaming as implementation action, where individual sectors and institutions commit to specific activities to achieve joint outcomes for the national AIDS and development responses.