Campylobacter spp. are regarded as the most common foodborne bacterial zoonosis in Europe, despite potential underestimation due to underreporting of cases. In France, C. jejuni is responsible for nearly 80% of human infections while C. coli accounts for around 15%. The economic burden of campylobacteriosis has been estimated to 2.4 billion euros annually in Europe, with estimates of £50 million in 2008–2009 in the United Kingdom and 82 million euros in the Netherlands in 2011.Pathogen source attribution studies are a useful tool for identifying reservoirs of human infection. Based on Multilocus Sequence Typing (MLST) data, such studies have identified chicken as a major source of C. jejuni human infection. The use of whole genome sequence-based typing methods offers potential to improve the precision of attribution beyond that which is possible from 7 MLST loci. Using published data and 156 novel C. jejuni genomes sequenced in this study, the researchers performed probabilistic host source attribution of clinical C. jejuni isolates from France using three types of genotype data: comparative genomic fingerprints; MLST genes; 15 host segregating genes previously identified by whole genome sequencing. Consistent with previous studies, chicken was an important source of campylobacteriosis in France (31–63% of clinical isolates assigned). There was also evidence that ruminants are a source (22–55% of clinical isolates assigned), suggesting that further investigation of potential transmission routes from ruminants to human would be useful.