This is a compendium of recent work by Prohofsky and his collaborators on different aspects of bond disruption, base pair separation, melting, and drug dissociation of DNA. It contains a thorough exposition of the effective harmonic bond theory coupled to a Bogolyubov-Feynman variational Ansatz that forms the core of Prohofsky's approach to the statistical mechanical analysis of the subject. The book is not, however, meant to be an introduction of the method, so all the technical details are conveniently relegated to the appendices. They are nevertheless sufficiently detailed so that the interested reader will find them a good starting point to actually learn something about the method itself