This book reviews advances in important and practically relevant homogeneous catalytic transformations, such as single-site olefin polymerizations and chemo- and stereo-selective oxidations. Close attention is paid to the experimental investigation of the active sites of catalytic oxidation systems and their mechanisms. Major subjects include the applications of NMR and EPR spectroscopic techniques and data obtained by other physical methods. The book addresses a broad readership and focus on widespread techniques available in labs with NMR and EPR spectrometers.