Aerospace and aeronautical systems are becoming ever more complex due to an increasing demand for the integration of multipurpose functionality and the availability of advanced technological solutions. These systems are required to perform several concurrent tasks such as operational parameters monitoring (temperature, pressure, strain, vibration, acceleration, altitude, etc.) and structural integrity diagnosis and prognosis, to name a few. All these functionalities require dedicated sensing hardware with the corresponding increase in complexity, cost, weight and failure rate probability. The progress made in optics and photonics in the last decades has provided a diverse range of sensing solutions, which present a reliable alternative to other sensing principles due to their reduced dimensions and cost, low power, flexibility, electrochemical inertness, immunity to electromagnetic interference, high sensitivity, and multipoint and remote sensing capabilities. This way, optical sensors are starting to play an important role in spacecraft and earth orbiting manmade objects, either in local or remote sensing applications. These sensors are typically involved with positional control of the spacecraft and detection of remote objects or environmental conditions locally or in the distance. These sensors can be viewed as active, or passive depending on their ability to illuminate the object of interest or just receive its emitted or scattered light respectively. In either situation the detector is usually composed of one or an array of optical detectors depending on the type of measurement we want to achieve either a single signal or a spectrum. In this chapter, we will be addressing advanced optical sensors being implemented in the aerospace industry with emphasis on the fundamental principles they rely on and the used materials. To this end, we will be describing the working principles of a wide range of highly sensitive advanced photodetectors, fibre Bragg gratings, photonic crystal fibres, diffraction gratings, optical microelectromechanical structures, piezo-optical sensors and transducers, interferometers and spectrometers. All these devices have found application in the aerospace industry and are being used to perform a wide range of functionalities, e. g. implemented in applications such as structural health monitoring, gyroscopes, inertial navigation systems, etc. Our approach will remain as broad and reader friendly as possible, leaving out mathematical abstractions whenever possible, and often relying on simulations and graphical interpretations to demonstrate the involved phenomena. This way, we intend to establish an easy to follow reading experience and, hopefully, a seamless connection to subsequent chapters of the book.