Gabon is divided into provinces, which are subdivided into départements (departments). I found a number of sources for the departments of Gabon (sources [2-7], and Wikipedia), but they disagree with each other. The SALB data seem to cover the facts best, so they are the basis for the table below.

Change history:

1975: Territorial administration of Gabon underwent a reform, resulting in the following 37 departments (source [1]).

~1996-2000: Eleven new departments created. Sorin Cosoveanu has analyzed the splits as follows: Léconi-Djoué department split into Bayi-Brikolo, Djoué, Lékabi-Léwolo, and Lékoni-Lékori; Djouori-Agnili department split from Plateaux; Doutsila and Mongo departments split from Mougoutsi; Louetsi-Bibaka department split from Boumi-Louetsi; Mougalaba department split from Douya-Onoye; Offoué-Onoye department split from Lolo-Bouenguidi; Ogooué-Létili department split from Lékoko. Libreville commune may have existed before this date, but if not, it would have been split from Komo-Mondah.

Sources:

1. [1] Géographie et Cartographie du Gabon: atlas illustré, by Jacques Barret, EDICEF, Paris, 1983.
2. [2] SALB project, attributed to Institut National de Cartographie; first draft dated 2000, second draft dated 2005, with updates made 2003-01-15 (Libreville, correcting a misunderstanding) and 2003-04-03 (Bayi-Brikolo, Mougalaba, and Mongo).
3. [3] Consulate of Gabon in France  (retrieved 2009-04-06).
4. [4] Internet Gabon  (dated 2008, retrieved 2009-04-06).
5. [5] Journal Officiel  de la République Gabonaise: Jan. 1997 (retrieved 2009-04-06).
6. [6] Gabon National Assembly  website (retrieved 2009-04-06).
7. [7] legabon.org  (retrieved 2009-04-06).