The rumen microbes are usually divided into three distinct groups based on their habitats: the planktonic microbiota, feed particle associated microbiota, and the epimural microbiota. Among these three groups of microorganisms, the epimural community is the least studied and understood. Although the epimural microbiota only accounts for 1-2% of the total rumen microbial population, their functional importance should not be neglected. The members of epimural microbiota are the key players participating in oxygen scavenging, tissue recycling, urea metabolism, and nutrient transportation. The recent development of nucleic acid sequencing techniques has enabled us to better explore the composition and functional of this community. This chapter summarizes the current knowledge on the rumen epimural microbial community including its diversity, ecology, functions, and their relationships with host physiology. It also discusses the current challenges regarding the study of this microbial community. Finally, knowledge gaps and future perspectives for this research area are addressed.