A broad range of hydrocarbons and oxygenated products can be synthesized catalytically from CO and H2produced by the gasification of coal, Since the earliest examples of such chemistry were reported by Fischer and Tropsch [1, 2] in 1926, the nonselective generation of organic compounds via the hydrogenation of CO has become known as Fischer-Tropsch synthesis. In the intervening 54 years, many efforts have been made to identify the mechanism by which reactants are converted to products. These studies have been motivated in large measure by the desire to understand how catalyst composition and reaction conditions govern the distribution of products formed. A brief review of the mechanistic hypotheses developed prior to 1970 will be presented here to serve as background for a discussion of more recent ideas, Details concerning the earlier studies can be found in a number of reviews [3–15] published previously.