Roadkill is a wild animal that has been killed by collision with motor vehicles. Wildlife-vehicle collisions (WVC) have increasingly been the topic of academic research to understand the causes, and how they can be mitigated.

Essentially non-existent before the advent of mechanized transport, roadkill is associated with increasing automobile speed in the early 20th century. In 1920, naturalist Joseph Grinnell wrote of his observations in the state of California that "this is a relatively new source of fatality; and if one were to estimate the entire mileage of such roads in the state, the mortality must mount into the hundreds and perhaps thousands every 24 hours."

In Europe and North America, deer are the animal most likely to cause vehicle damage.

The development of roads affects wildlife by altering and isolating habitat and populations, deterring the movement of wildlife, and resulting in extensive wildlife mortality. One writer states that "our insulated industrialized culture keeps us disconnected from life beyond our windshields." Driving "mindlessly" without paying attention to the movements of others in the vehicle's path, driving at speeds that do not allow stopping, and distractions contribute to the death toll. Moreover, a culture of indifference and hopelessness is created if people learn to ignore lifeless bodies on roads.

A study in Ontario, Canada in 1996 found many reptiles killed on portions of the road where vehicle tires do not usually pass over, which led to the inference that some drivers intentionally run over reptiles. To verify this hypothesis, research in 2007 found that 2.7% of drivers intentionally hit reptile decoys masquerading as snakes and turtles. Several drivers were seen to speed up when aiming for the decoys. Male drivers hit the reptile decoys more often than female drivers. However, 3.4% of male drivers and 3% of female drivers stopped to rescue the reptile decoys.

On roadways where rumble strips are installed to provide a tactile vibration alerting drivers when drifting from their lane, the rumble strips may accumulate road salt in regions where it is used. The excess salt can accumulate and attract both small and large wildlife in search of salt licks; these animals are at great risk of becoming roadkill or causing accidents.

Very large numbers of mammals, birds, reptiles, amphibians and invertebrates are killed on the world's roads every day. A Humane Society volunteer survey conducted over three Memorial Day weekends in the 1960s estimated that one million vertebrate animals are killed by vehicular traffic daily in the United States. A 2008 Federal Highway Administration report estimates that 1 to 2 million accidents occur each year between large animals and vehicles. Extrapolating globally based on total length of roads, roughly 5.5 million vertebrates are killed per day, or over 2 billion annually.

The estimated number of birds killed on the roads in different European countries ranges from 350,000 to 27 million, depending on the factors such as the geography of the country and bird migration paths.