Although there is a great deal of information online about dual citizenship by descent for a number of different countries (Italy, Poland, etc.), there is not much at all for France. Here is an interesting article about a resident of Quebec (Canada) making a claim for French citizenship based on descent from French ancestors 400 years ago! Although the claim was rejected, the French consulate did acknowledge that a citizenship claim derived from a French ancestor who immigrated after the 1763 treaty with Britain could theoretically succeed. This means, of course, that Americans, Canadians, and others with more recent French ancestors (such as parents or grandparents) should be able to claim French citizenship.
http://www.canada.com/ottawacitizen/new ... 41438934d8