In recent times Optical Fibre Interferometric Sensors have found application in a number of important areas such as defense and remote detection applications, structural health monitoring and in the electricity transmission and distribution industries. Typically Optical fibre sensors have relatively small sensitivities and it is for this reason that optical fibre sensors and interferometric detection systems have developed hand-in hand. Often the greatest gains in system sensitivity are realized through careful design and implementation of the interferometric detection system. In particular polarisation control, and common mode rejection become important design considerations without which signal to noise performance can degrade significantly. This book details the benefits and some practical design considerations for optimizing optical fibre sensor systems for both polarisation control and common mode rejection. This includes studies and analysis of a practical optical fibre voltage sensor system and the latest manifestations of polarisation controlling optical fibres.