Papillomavirus induce benign tumours (papillomas) in a variety of animals. The papillomas generally regress but occassionally persist and may eventually progress to squamous cell carcinoma. One of the most extensively studies papillomaviruses is bovine papillomavirus type 4 (BPV4). BPV-4 induces papillomas of the upper alimentary canal which are at high risk of progressing to cancer in cattle eating bracken fern. In this review, several aspects of the biology of the virus are described and compared with other papillomavirus systems, including regulation of transcription of the viral oncogenes, function of the viral oncoproteins, cooperation between virus and chemical cofactors, and prophylactic and therapeutic vaccination programmes.