Poultry is a major reservoir of Campylobacter jejuni, which is currently the leading cause of acute bacterial diarrhoea in western countries. This results in substantial accumulated economic loss due clinical costs and lost working hours. In developed countries reinforcement of hygienic practices and consumer education have so far been inadequate to significantly decrease numbers of human cases of campylobacteriosis. The control of poultry associated infection in humans may also depend upon the control of Campylobacter colonization in broiler flocks. However, sources of C. jejuni and the transmission routes through which broilers become colonized are not clearly defined. A better understanding of C. jejuni epidemiology is urgently needed. This review summarizes current theories on the epidemiology of C jejuni broiler colonization.