PHOSFOS (Photonic Skins For Optical Sensing) develops and builds on a new paradigm for optical sensors integrated in an unprecedented manner with opto-electronic and electronic circuitry in flexible and stretchable skins for applications in diverse fields including structural health monitoring, automotive industry, aeronautics and aerospace, robotics, healthcare etc. PHOSFOS intends to develop a technology that provides an answer to essential issues that have so far prevented fibre sensors from penetrating the market, which include packaging, fully-fledged system integration, optical coupling and interfacing, dependable strain transfer and reliability. The project positions itself at the pre-competitive intersection of optical fibre sensing and integrated optics. It aims at developing a flexible and stretchable foil in which all necessary optical sensing elements can be integrated; that if relevant to the application can include optical and electrical powering as well as onboard signal processing and wireless communications; that can be wrapped around irregularly shaped objects; that will allow quasi-distributed sensing. To do so the sensing elements in PHOSFOS will rely on special highly birefringent micro-structured optical fibres (MSF) and polymer optical fibres (POF) with fibre Bragg gratings. The silica fibres will be designed to exhibit almost zero temperature sensitivity whereas POF fibres will be used for their very specific property that their length can be stretched up to 300 % before breaking. The optimal Bragg grating writing technology in these fibres, both silica and POF, will be developed. PHOSFOS will focus on embedding these into the sensing skin and on the optical coupling/interfacing to the peripheral opto-electronics and electronics. PHOSFOS will end with 2 proof-of-concept demonstrators, a first targeting structural health monitoring of civil engineering structures, the second aiming at the automotive industry.