Landfills are the most widely utilized solid waste management option. But, what is in our landfills? Although findings differ slightly, in 2006 approximately 26 percent of materials entering landfills were paper products, 18 percent food scraps, 16 percent plastic, 9 percent rubber, leather, and other textiles, 7 percent each of yard waste, metals, and wood, and 6 percent glass. This does not, however, reflect actual landfill content at any point in time since some materials decompose faster, or compact better, than others.

Prior to landfills, most Americans lived in sparsely populated rural farming communities, burning the majority of their garbage in open dumps. Early landfills took the place of those dumps, with no effort to compact or cover up the waste. Over the last few decades, these dumps have been replaced with landfills which are more sophisticated in design and regulated in every aspect, from siting to filling to closing.

Modern landfills are constructed with a number of safeguards, including clay or plastic lining to contain leachate. The waste is typically compacted in order to increase its density and stability, and covered to prevent any attraction of pests. As organic waste decomposes it generates gases, including methane which is a greenhouse gas. As portions of a landfill (called cells) are closed, pipes are often installed to vent or incinerate the gases before they can diffuse into the ground, increasing the risk of explosion. The gas can also be collected and used to generate electricity.

The number of landfills in the United States has steadily declined over the last 2 decades (but has remained relatively constant since 2002); yet, the average size of landfills has increased. Overall, landfill capacity appears to be sufficient, although it is limited in some areas. Building new landfills, however, is an expensive and time-consuming process, primarily due to community opposition (the NIMBY syndrome, not-in-my-backyard) and regulations requiring increasingly sophisticated engineering measures to ensure safety.