Biosecurity plays a pivotal role in maintaining the health of poultry. Biosecurity is the protection of birds from disease-causing agents. This chapter reviews the range of biosecurity measures required to maintain the health of laying hens. It talks about separation of birds which is an important measure. It reviews disease identification and detection, including the identification of specific diseases and vaccination regimes for prevention or treatment. Finally, this chapter discusses in detail the common diseases of egg-laying chickens, some of them being respiratory diseases, diseases related to the nervous system, the intestinal system, etc.