There are a series of reactions such as isomerization, alkylation, dimerization of olefins, condensation, etc, which are catalyzed by bases. Solid base catalysts are competitive with respect to solid acid catalyst for carrying out reactions which can be catalyzed by either acids or bases. Solid bases can successfuly catalyze transformations of organic substrates containing heteroatoms, such as N, O, and S. Solid acids, which can also catalyze these reactions, often are poisoned by those substrates. Moreover, in some cases, such as olefin and alkyne isomerizations, it is possible by using bases to achieve stereochemical control. This has impulsed researches to look for very strong solid base catalysts, i.e., superbasic solids, such as supported alkaline metals. These, while active at moderate temperatures, present a major drawback derived from their relatively low stability and frequent catalyst regenerations. However, there are a significant number of interesting reactions which can also be catalyzed by bases with medium strength. In this case, the use of a very strong base catalyst can be disadvantageous because it can also catalyze other, non desired, more demanding reactions, with the corresponding decrease in selectivity to the desired product. Furthermore, in some processes, it can become more critical to adequately control the acid-base pairs than to achieve a very strong type of basic sites.