Campylobacter jejuni is an important zoonotic agent in Europe and many other countries worldwide. The bacterium causes gastrointestinal infection after consumption of contaminated food. Poultry meat is the main source of infections and poultry houses can be a reservoir of C. jejuni. It is suggested that horizontal transmission plays a major role in the spread of C. jejuni within and between poultry flocks. Probable sources of infection include colonized birds, contaminated faeces, feed, litter, water, equipments and transport vehicles or even wild birds and insects. However, the role of laying hens in transmission is neglected. Therefore, this book will give insight on the laying hens and their environments as a reservoir of C. jejuni and its role in Campylobacter transmission in and between flocks then to human.