Monster Attack

Earth Defense Force has roughly five separate continuities as of 2024. However, in general, all entries in the series share a similar basic premise, following the Earth Defense Force (EDF), a specialized multinational defense force established and supported by every country and staffed by the world's militaries, tasked with defending Earth and humanity from external threats. The vast majority of Earth Defense Force installments are set after the discovery of the Ravagers, an intelligent and organized alien race, with the formation of the EDF sometimes explained as being a precautionary measure. The Ravagers prove to be hostile and attempt to invade Earth, deploying massive insectoids such as ants, ticks, pillbugs, beetles, hornets, and spiders to destroy Earth and exterminate humanity; this prompts the full-scale deployment of the EDF to fight back and repel the alien invasion.

The series installments are mostly set during the 2017 invasion, during later invasions in 2019 and 2025, or, in different continuities such as the one introduced in Earth Defense Force 5, 2022 and 2026. Several conflicts also feature alien races and enemy types distinct from the Ravagers and the insects, including the bipedal frog-like Colonists (their "resemblance" to humans based on generic characteristics such as having two eyes is a running gag), the advanced grey alien-inspired Cosmonauts, the reality-bending but genocidal Primers, assorted robots and probes fielded by the aliens, and various kaiju.

Despite generally mixed reviews, the Earth Defense Force series, particularly from Earth Defense Force 2017 and onwards, has been described as having a cult following. Joe Juba of Game Informer defined Earth Defense Force 2017 as a cult classic, stating that "the developers at Sandlot clearly want to tell a story about humanity's struggle against giant invading ants and robots, and the passion for that story shines through despite its technical shortcomings"; in reviewing Earth Defense Force 5 five years later, he similarly opined that the series has "always had a single-minded commitment to one simple truth: It's fun to use weird weapons to blast lots of aliens." Though James Stephanie Sterling gave Earth Defense Force 2025 a negative review, she did acknowledge that the series "has managed to earn itself a fierce cult following through audacity alone".