In a general sense contingency can be described as “That what is possible but not necessary. What is contingent, could also be different.” I would not go as far as Basanta in saying the organizational structure and similar features are determined by its context since the term determined suggest that things could not have been different. Contingency theory place emphasis on the relation between that what is and its history. In terms of society everything is contingent: elements, structures, relations and operations. All these evolve in interplay with each other; an interplay that helps to explain that what is and how it came into being. This, however, does not imply that the particular context determines the further development; chance and coincidence do play a role. A more extensive elaboration on the concept of contingency, its relation with power relations, and its embedding in social systems theory (Luhmann) and post-structuralism can be found in the article “Power and contingency in planning”.
Dear Catalina, contingency theory has another very important take, which comes directly from the works by S. J. Gould - applied both to nature and society.
As you know, the very idea of contingency (theory) stands over against the idea of sheer necessity. In the background, however, lies a much deeper debate which is between: are the world and nature continuous, or else, are they discrete? If you follow up the very question it will lead to forwards to the discussion about continuity versus discrete reality.
I am personally very much interested in the issue you mention.
(Between brackets: with all due respect to Amanda, forget about Luhmann: that is the view of society without subjects…).