Landfills are a vital component of our waste handling processes. Our lack of knowledge on the microbial processes in these systems, however, hampers our ability to design the next generation of landfills that: (1) enhance the rate and extent of waste decomposition, (2) produce byproducts of some value (e.g., methane that can be used for energy generation), and, (3) minimize their overall impact on driving climate change through the emission of greenhouse gases. In this review, the current state of knowledge the microbial community structure and activity in both the refuse and overlying cover soils is discussed, and suggestions provided for future research in this critical aspect of our infrastructure.