This chapter reviews poultry welfare monitoring, specifically focusing on wearable technologies. It begins by discussing the use of radio-frequency identification technology (RFID) systems in chickens and other housing systems. The chapter then goes on to address wearable sensors and accelerometers, focusing on the effects of these sensors on chicken behaviour and how the different behavioural activities can be classified. It also highlights how these sensors can be used for monitoring disease and euthanasia in chickens, as well as monitoring perching, jumping, falls and collision. A section on the importance of using wearable technologies for measuring physical activity levels is also included, which is then followed by a case study that analyses outdoor stocking density in free-range laying hens. The chapter concludes by providing potential areas for future research as well as giving examples of resources for further information on the subject.