The Porphyrins, Volume IV: Physical Chemistry, Part B focuses on the physical chemistry of porphyrins, their precursors, catabolic derivatives, and related compounds. The book covers nuclear magnetic resonance (NMR) spectroscopy of diamagnetic and paramagnetic porphyrins and electron nuclear double resonance (ENDOR) spectroscopy of chlorophylls and related systems. It also encompasses electron spin resonance (ESR) spectroscopy of porphyrin pi cations and anions, porphyrin excited states, metalloporphyrins, hemoproteins, and hemes. This volume is organized into nine chapters and begins with an overview of NMR theory and the use of NMR spectroscopy to study diamagnetic porphyrins and paramagnetic metalloporphyrins. The discussion then shifts to the theory of ENDOR spectroscopy and the application of ENDOR spectroscopy to analysis of chlorophylls, ESR of pi cations and anions of porphyrins as well as porphyrin excited states, and electron paramagnetic resonance and Mossbauer spectra of hemoproteins. The reader is also introduced to ESR and the electronic structure of metalloporphyrins. A chapter on Mossbauer spectroscopy of iron porphyrins concludes the book. This book is a valuable resource for inorganic, organic, physical, and biochemists interested in the physical chemistry of porphyrins.