This book focuses on observing magnetic fields in order to understand their role in star and planet formation. Polarimetry observers will gain a better understanding of all the various techniques, especially those beyond what they themselves use. Theorists will gain an understanding of exactly what one can infer from the observational data, including both the limitations and the power of the different techniques. Readers not actively involved in star formation research will gain a clear understanding of the possible roles played by magnetic fields and the current state of the observational field. The book provides a foundation for future research in this field.