Waste compaction is the process of compacting waste, reducing it in size. Trash compactors and waste collection vehicles compress waste so that more can be stored in the same space. The waste is compacted again, more thoroughly, in the landfill "Landfill (garbage)") to conserve space and extend the life of the landfill.

Compaction before landfills is usually beneficial, both for the people who dispose of them and for the company that collects them. This is because trash companies typically charge by volume or require the use of standard volume containers, and compaction allows more waste to fit in the same space. Trash compactors are available for both residential and commercial use. Compacting trash after collection allows more waste to fit inside the collection vehicle, meaning fewer trips to a landfill are required "Landfill (garbage)") or transfer station&action=edit&redlink=1 "Transfer station (waste management) (not yet drafted)"). The collection company also incurs lower landfill fees, if the landfill charges by volume.[1]​.

A landfill compaction vehicle has two main functions: spreading waste evenly in layers over the landfill and compacting the waste to reduce its volume and help stabilize the landfill. Proper waste compaction includes the process of using a landfill compactor with steel wheels/drums to crush, tear, and press various items in the waste stream so that they consume a minimum volume of landfill airspace. The higher the compaction rate, the more trash the landfill can receive and store. This will also reduce landslides, cave-ins, and minimize the risk of landfill gas explosions (see landfill gas migration).

Primary compaction occurs by the landfill compactors' steel teeth on the wheel drums. Special teeth can penetrate debris and provide a focused compression point, providing compaction and higher density. Tooth ground pressure can exceed 4,000 pounds per square inch (28,000 kPa) (PSI). The design of the machine and more importantly the wheels and teeth is very critical in compaction. Power transmission from the engine to the wheel drums is another key factor in compactors, depending on the application and size of the landfill, the correct size and configuration of the machine must be selected.

Uncompacted garbage takes up up to 20 times more landfill space than compacted garbage. Waste transportation costs are reduced with fewer or smaller trash containers, and container collection frequency can be reduced by 50 percent. A side effect of waste compaction is that important items, such as evidence in a crime, can be difficult to recover from the trash. Due to reduced oxygenation, the biodegradation of organic waste is also slowed down.