Overexploitation, also called overharvesting or ecological overshoot, refers to harvesting a renewable resource to the point of diminishing returns. Continued overexploitation can lead to the destruction of the resource, as it will be unable to replenish. The term applies to natural resources such as water aquifers, grazing pastures and forests, wild medicinal plants, fish stocks and other wildlife.

In ecology, overexploitation describes one of the five main activities threatening global biodiversity. Ecologists use the term to describe populations that are harvested at an unsustainable rate, given their natural rates of mortality and capacities for reproduction. This can result in extinction at the population level and even extinction of whole species. In conservation biology, the term is usually used in the context of human economic activity that involves the taking of biological resources, or organisms, in larger numbers than their populations can withstand. The term is also used and defined somewhat differently in fisheries, hydrology and natural resource management.

Overexploitation can lead to resource destruction, including extinctions. However, it is also possible for overexploitation to be sustainable, as discussed below in the section on fisheries. In the context of fishing, the term overfishing can be used instead of overexploitation, as can overgrazing in stock management, overlogging in forest management, overdrafting in aquifer management, and endangered species in species monitoring. Overexploitation is not an activity limited to humans. Introduced predators and herbivores, for example, can overexploit native flora and fauna.

The concern about overexploitation, while relatively recent in the annals of modern environmental awareness, traces back to ancient practices embedded in human history. Contrary to the notion that overexploitation is an exclusively contemporary issue, the phenomenon has been documented for millennia and is not limited to human activities alone. Historical evidence reveals that various cultures and societies have engaged in practices leading to the overuse of natural resources, sometimes with drastic consequences.

One poignant example can be found in the ceremonial cloaks of Hawaiian kings, which were adorned with the feathers of the now-extinct mamo bird. Crafting a single cloak required the feathers of approximately 70,000 adult mamo birds, illustrating a staggering scale of resource extraction that ultimately contributed to its extinction. This instance underscores how cultural traditions and their associated demands can sometimes precipitate the overexploitation of a species to the brink of extinction.

Similarly, the story of the dodo bird from Mauritius provides another clear example of overexploitation. The dodo, a flightless bird, exhibited a lack of fear toward predators, including humans, making it exceptionally vulnerable to hunting. The dodo's naivety and the absence of natural defenses against human hunters and introduced species led to its rapid extinction. This case offers insight into how certain species, particularly those isolated on islands, can be disproportionately affected by human activities due to their evolutionary adaptations.

Hunting has long been a vital human activity for survival, providing food, clothing, and tools. However, the history of hunting also includes episodes of overexploitation, particularly in the form of overhunting. The overkill hypothesis, which addresses the Quaternary extinction events, explains the relatively rapid extinction of megafauna. This hypothesis suggests that these extinctions were closely linked to human migration and population growth. One of the most compelling pieces of evidence supporting this theory is that approximately 80% of North American large mammal species disappeared within just approximately a thousand years of humans arriving in the Western Hemisphere. This rapid disappearance indicates a significant impact of human activity on these species, underscoring the profound influence humans have had on their environment throughout history.

The fastest-ever recorded extinction of megafauna occurred in New Zealand. By 1500 AD, a mere 200 years after the first human settlements, ten species of the giant moa birds were driven to extinction by the Māori. This rapid extinction underscores the significant impact humans can have on native wildlife, especially in isolated ecosystems like New Zealand. The Māori, relying on the moa as a primary food source and for resources such as feathers and bones, hunted these birds extensively. The moa's inability to fly and their size, which made them easier targets, contributed to their rapid decline. This event serves as a cautionary tale about the delicate balance between human activity and biodiversity and highlights the potential consequences of over-hunting and habitat destruction. A second wave of extinctions occurred later with European settlement. This period marked significant ecological disruption, largely due to the introduction of new species and land-use changes. European settlers brought with them animals such as rats, cats, and stoats, which preyed upon native birds and other wildlife. Additionally, deforestation for agriculture significantly altered the habitats of many endemic species. These combined factors accelerated the decline of New Zealand's unique biodiversity, leading to the extinction of several more species. The European settlement period serves as a poignant example of how human activities can drastically impact natural ecosystems.