自然保护区指相关法律创建的以保护生物多样性的环境、地质构造以及水资源等自然综合体的核心区域。在区域内，人类的各种活动受到不同程度的限制，以确保一区域内的保护对象保持无人为干预的自然发展状况。自然保护区的设立必须以保护包含某个核心对象为目标。地域为陆地、水体；对象为具有代表性的生态系统、珍稀濒危动物的天然集中分布区、水源涵养区、具有典型代表性地质构造、地质剖面和化石资源等。

世界上最早创建的自然保护区为美国加利福尼亚州西迈山谷的红杉树保护区，在1864年创建。

A nature reserve (natural reserve, bioreserve, (natural/nature) preserve or (national/nature) conserve) is a protected area of importance for wildlife, flora, fauna or features of geological or other special interest, which is reserved and managed for conservation and to provide special opportunities for study or research. Nature reserves may be designated by government institutions in some countries, or by private landowners, such as charities and research institutions, regardless of nationality. Nature reserves fall into different IUCN categories depending on the level of protection afforded by local laws.