I have written this book to fill a void between theory and practice, a void that I perceived while conducting my own research and development of components and instruments over the last years. In the chapters that follow I have pulled materials from the technical and patent literature that are relevant to the understanding and practice of polarization optics in telecommunications, material that is often known by the respective experts in industry and academia but is rarely if ever found in one place. By bringing this material into one monograph, and by applying a single formal ism throughout, I hope to create a “base level” upon which future research and development can grow. Polarization optics in telecommunications is an ever evolving? eld. Each year significant advancements are made, punctuated by important discoveries. The references upon which this book is based are only a snapshot in time. Areas that remain unresolved at the time of publication may very well clarified in the years to come. Moreover, the focus of the field changes in time: for instance, there have been few passive nonreciprocal component advancements reported in the last few years, but PMD and PDL advancement continues with only modest abatement.