Abstract: The concept of and root microbiota commonalities was already presented by Ramirez-Puebla et al.(2013); they discussed a lot of similar functional traits, host-bacteria interactions as well as evolutionary trends but also several differences. Based on deeper insights obtained by omics technologies, Mendes and Raaijmakers (2015) recently presented their concept that the structure and function of rhizosphere and gut microbiomes showcross-kingdom similarities. In parallel, Hacquard et al. (2015) analyzed of the microbiota composition across plant and animal kingdoms and found only little overlap comparing fish gut and plant root communities. They explained the differences by various start inoculants and abiotic, niche-specific factors. In this context, to establish concepts is pivotal in microbial ecology for the critical evaluation of the immense amount of data obtained by omics technologies, not only for conceptual work in microbial ecological theories(Prosseretal.,2007), but also for translational fields such as biocontrol of pathogens (Bergetal.,2013). Therefore, we would like to extend the concept of cross-kingdom similarities presented by Mendes and Raaijmakers (2015) to an ecological context, which is shared for host-associated microbiomes beyond the boundaries of their respective kingdoms. Finally, we discuss the impact and implications of microbiome ecology on biocontrol of pathogens in plants and in humans.