In recent years it has been recognised that experiments with isomers of stable nuclei offer great scientific opportunities for the study of rare but important nuclear species. This field is now considered as one of the priority areas for nuclear astrophysics and gamma-ray laser-technique for the coming decade. Gamma ray line astronomy has a unique potential to provide information on nuclear processes and high energy interaction going on presently in the universe. Despite many negative conclusions the investigators have found more obvious proposals, and there are more potential approaches to x-ray laser program today than ever before. The fundamental precept is that the very highest densities of energy storage would be found within the isomeric state of the nucleus, but the central problem of x-ray laser is to pump the gadget without heating the lattice and so destroying the Mössbauer and Bormann effect. On 200 pages this book deals with the most recent state of the photoexcitation of isomers and contains numerous experimental results of the last fifty years. The book aims at illustrating the usefulness of isomer studies in a broad region of applications. It addresses scientists and engineers, who are interested in applying nuclear techniques in the mentioned fields.