The inclusion of small guest molecules within suitable host compounds results in constrained systems that imbue novel properties upon the incarcerated organic substrates. Supramolecular tactics are becoming widely employed and this treatise spotlights them. Often, the impact of encapsulation on product formation is substantial. The use of constrained systems offers the means to steer reactions along desired pathways. A broad overview of various supramolecular approaches aimed to manipulate chemical reactions are featured. The following topics are covered in detail: - general concepts governing the assembly of the substrate with the reaction vessel - preparation of molecular reactors - stabilization of reactive intermediates - reactions in water, in organic solvents, and in the solid state - photochemical reactions - reactions with unusual regioselectivity Molecular Encapsulation: Organic Reactions in Constrained Systems is an essential guide to the art of changing the outcome and the selectivity of a chemical reaction using nano-sized reaction vessels. It will find a place on the bookshelves of students and researchers working in the areas of supramolecular chemistry, nanotechnology, organic and pharmaceutical chemistry, and materials science as well.