Methane is a potent greenhouse gas with a global warming potential 25 times greater than carbon dioxide over a one hundred year time span. Enteric fermentation by ruminant livestock is Australia’s dominant source of anthropogenic methane pollution, estimated to be 52% of national anthropogenic methane produced per annum. Methane generation is a result of complex microbial interactions in the rumen. Currently, the possibility of a co-occurring microbial methane sink has not been reported. This project aimed to explore the ecology and function of methane oxidising bacteria in the rumen of Australian cattle. Molecular screening methods were developed to characterise the biodiversity of methane oxidising bacteria in the rumen. This was done using a combination of denaturing gradient gel electrophoresis (DGGE), clone library generation, sequencing, phylogenetics and quantitative polymerase chain reaction (qPCR) of 16S rRNA and functional genetic markers. In two separate groups of grain-fed Bos indicus cattle (n = 8), simple communities of putative methane oxidising Methylobacter and Methylocystis species were identified at 1 x 10³ – 1 x 10⁵ 16S rRNA gene copies per mL of rumen fluid. Novel culture-dependent methods were developed to enrich methanotrophs under in vitro anaerobic rumen-like conditions run semicontinuously in a chemostat. Methanogenic archaea and putative methane oxidising bacteria were co-cultured for up to 7 days. Methanogen and methanotroph populations were monitored with qPCR targeting the 16S rRNA gene, and methane production was monitored with gas chromatography. DNA based stable isotope probing with ¹³CH₄ was used to confirm methane consumption by Methylobacter species, as both DGGE and qPCR demonstrated ¹³C labelling of Methylobacter DNA. These findings suggest that previously undiscovered anaerobic methane oxidising bacteria may act as a methane sink in the rumen. These organisms may be potential candidates for a probiotic approach to mitigating methane pollution by enteric fermentation.