This is the first comprehensive practical guide for people who perform EPR measurements, or supervise the use of EPR spectroscopy, and want to obtain quantitative results. No existing book provides this level of practical guidance to ensure successful use of EPR. This meets the growing need in both industrial and academic research to provide meaningful and accurate quantitative results from EPR experiments. Discussed are the various sample-related, instrument-related and software-related aspects for obtaining useful quantitative results from EPR experiments. Some specific items discussed include: choosing a reference standard, resonator considerations (Q, B1, Bm), power saturation characteristics, sample positioning, and finally, putting all the factors together to provide a calculation model for obtaining an accurate spin concentration of a sample. Both relative intensity quantification and the absolute spin concentration of EPR samples are covered as well. Numerous pictures of the effect of instrument parameters on EPR spectra are included and careful attention to the guidance given in this book will ensure quantitatively accurate EPR spectra.