Combinatorial chemistry comprises chemical synthetic methods that make it possible to prepare a large number (tens to thousands or even millions) of compounds in a single process. These compound libraries can be made as mixtures, sets of individual compounds or chemical structures generated by computer software. Combinatorial chemistry can be used for the synthesis of small molecules and for peptides. Strategies that allow identification of useful components of the libraries are also part of combinatorial chemistry. The methods used in combinatorial chemistry are applied outside chemistry, too. History Combinatorial chemistry had been invented by Furka Á (Eötvös Loránd University Budapest Hungary) who described the principle of it, the combinatorial synthesis and a deconvolution procedure in a document that was notarized in 1982. The principle of the combinatorial method is: synthesize a multi-component compound mixture (combinatorial library) in a single stepwise procedure and screen it to find drug candidates or other kinds of useful compounds also in a single process. The most important innovation of the combinatorial method is to use mixtures in the synthesis and screening that ensures the high productivity of the process. Motivations that led to the invention had been published in 2002. Introduction Synthesis of molecules in a combinatorial fashion can quickly lead to large numbers of molecules. For example, a molecule with three points of diversity (R1, R2, and R3) can generate possible structures, where , , and are the numbers of different substituents utilized. The basic principle of combinatorial chemistry is to prepare libraries of a very large number of compounds then identify the useful components of the libraries. Although combinatorial chemistry has only really been taken up by industry since the 1990s, its roots can be seen as far back as the 1960s when a researcher at Rockefeller University, Bruce Merrifield, started investigating the solid-phase synthesis of peptides. In its modern form, combinatorial chemistry has probably had its biggest impact in the pharmaceutical industry. Researchers attempting to optimize the activity profile of a compound create a 'library' of many different but related compounds. Advances in robotics have led to an industrial approach to combinatorial synthesis, enabling companies to routinely produce over 100,000 new and unique compounds per year. In order to handle the vast number of structural possibilities, researchers often create a 'virtual library', a computational enumeration of all possible structures of a given pharmacophore with all available reactants. Such a library can consist