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Lameness is the greatest health and welfare concern in sheep flocks in the U. K. This thesis presents research on epidemiology of lameness in sheep Most previous studies quantifying lameness and its causes are based on the premise that farmers can identify the causes of lameness and recognise lame versus sound sheep. In 2005, a postal questionnaire was sent to a random sample of English sheep farmers to investigate whether farmers could correctly name six common foot lesions in sheep (interdigital dermatitis (ID), footrot (FR), contagious ovine digital dermatitis (CODD), shelly hoof, foot abscess and toe granuloma) from a characteristic picture and a written description. The same questionnaire of six lesions was presented at a meeting of specialist sheep advisors, primarily veterinarians. Approximately 20% of farmers and 80% of sheep specialists named all 6 lesions correctly, indicating a gap in knowledge between sheep advisors and sheep farmers. In addition, farmers tended to name any hoof horn damage as footrot which might imply that some lame sheep receive incorrect treatment. Management factors associated with the prevalence of farmer estimated lameness (irrespective of farmer recognition of lesions) and the adjusted prevalence of lameness caused by ID and FR among flocks where farmers correctly recognised both lesions were investigated and compared in negative binomial regression models. Farmers who routinely foot trimmed and frequently footbathed their sheep reported a higher prevalence of lameness, ID and FR. Farmers who stocked their sheep at >8ewes/hectare reported a high prevalence of both lameness and ID whilst those who separated `some' or `all' lame sheep at pasture reported a low prevalence of both lameness and ID. Farmers in the east of England reported a lower prevalence of lameness, ID and FR compared with central England. A numerical rating locomotion scoring scale (0-6) was developed to monitor locomotion in sheep in a research setting. There was good agreement between and within trained observers using this scale. This scoring system was used in a longitudinal study on one farm, two groups of sheep (30 in each group) with different treatment regimes (antibiotic injection & antibiotic spray vs. foot trimming and antibiotic spray; and occasional footbathing) for lameness with FR and ID were followed for five weeks to investigate the temporal associations between ID, FR and the effect of different treatments on locomotion. From the examinations it was concluded that even mildly lame sheep can have FR and ID. In a multilevel linear mixed model, there was a significant association between ID, FR and locomotion score with the mean score of 0.25 increasing to 0.43 for sheep with ID and to 2.18 for sheep with FR. In addition, sheep that developed FR had a significantly raised locomotion score the week before FR became clinically apparent. Treatment with antibiotic injection and antibiotic spray significantly reduced the locomotion score of sheep the following week. The movie clips from the locomotion scoring reliability study were used to investigate farmer and sheep specialist recognition of lame sheep and decisions on whether to catch them. A group of farmers from three regions (Devon, Newark and Norfolk) and sheep specialists at a Sheep Veterinary Society meeting were shown eight movie clips of sheep with varying locomotion scores. Although the majority of farmers and sheep specialists identified mildly lame sheep with a locomotion score of 2, only 50% of them would catch such a sheep if it was the only lame sheep in the group. Most farmers and sheep specialists did not catch lame sheep until the lameness was locomotion score 3 or 4. The more frequently farmers caught lame sheep, and the milder the lameness when a decision to catch was taken, the lower the farmer reported prevalence of lameness in the flock. The research in this thesis suggests that farmers, who are the primary carers for lame sheep, do not always name foot lesions correctly and so sheep may receive inappropriate treatment for some lesions. In addition, whilst farmers and sheep specialists can recognise lame sheep, they do not always catch and treat mildly lame sheep. Farmers who caught all mildly lame sheep within a few days of seeing them lame reported a lower prevalence of lameness in their flock. This might be explained by the evidence from this thesis that mildly lame sheep can have FR or ID and so prompt treatment of these lame sheep reduces the prevalence and incidence of FR and ID.