We define microbiome engineers as species that modify the microbiome associated with other host species via changes in the physical environment, potentially including the creation of dispersal networks for microbiome consortia across multiple hosts. Grazers such as bison are indirect plant microbiome engineers through alteration of the structure of plant communities in grasslands and forests. They also can directly engineer plant microbiomes if they distribute microbial consortia. Direct engineering may include simpler examples such as the role of truffle-eating animals in structuring forest mycorrhizal communities, as well as more complex roles in structuring the evolution of bacterial, fungal, and viral microbiome networks. Grazers and browsers may have important historic and current roles in engineering microbiomes by (a) stabilizing and homogenizing microbiomes in their preferred plant species, and (b) selecting for microbiomes in their preferred plant species that are differentiated from microbiomes in plant species they rarely consume.