Pan-Africanism is a term which can have two separate, but related meanings.
In the first sense, Pan-Africanism is a movement of union and recognition of cultural similarity and commonality of interests of all of the countries of Africa, particularly sub-Saharan Africa ("black Africa"). Institutions to promote this are in existence, such as the African Union; Pan-Africanists applaud them but feel that they do not go nearly far enough.
In the second sense, Pan-Africanism is the idea that all black persons, wherever they are in the world, are first and foremost citizens of Africa. This has become a tenant of most black nationalist movements.
See also: Pan-African colours
An organization with the formal name "Pan-African Congress" held a meeting in 1919 in Paris. Prior to that the ideas of Pan-Africanism already circulated including at a conference of 1900 considered a prelude to later ones.
The most important leader of the early years was W.E.B. DuBois. Another was George Padmore.
As Africans gained independence from the colonialists, Pan-Africanists not only held meetings but started to head governments. Padmore served as a government official and Kwame Nkrumah and Sekou Toure were vital leaders who headed states.
Also in the 1960s an organization arose specifically for the fight against apartheid in South Africa. The Pan-African Congress was responsible for much of the radicalization of the fight against apartheid, because prior to it pacifist ideas held greater sway. The Pan-Africanist Congress was one of two U.N. recognized organizations connected to South Africa (sometimes referred to as "Azania") while the white-minority regime held power.
 (http://members.aol.com/aaprp/index2.html)All African People's Revolutionary Party and more Pan Africanist links
 (http://www.ufh.ac.za/collections/NAHECS/Liberation/pachome.htm)Archives of the Pan Africanist Congress of Azania
 (http://www.etext.org/Politics/MIM/countries/panafrican/index.html)Early Pan African documents and some writings of George Padmore