Natural history is a domain of inquiry involving organisms, including animals, fungi, and plants, in their natural environment, leaning more towards observational than experimental methods of study. A person who studies natural history is called a naturalist or natural historian.

Natural history encompasses scientific research but is not limited to it. It involves the systematic study of any category of natural objects or organisms, so while it dates from studies in the ancient Greco-Roman world and the mediaeval Arabic world, through to European Renaissance naturalists working in near isolation, today's natural history is a cross-discipline umbrella of many specialty sciences; e.g., geobiology has a strong multidisciplinary nature.

The meaning of the English term "natural history" (a calque of the Latin historia naturalis) has narrowed progressively with time, while, by contrast, the meaning of the related term "nature" has widened (see also History below).

In antiquity, "natural history" covered essentially anything connected with nature, or used materials drawn from nature, such as Pliny the Elder's encyclopedia of this title, published c. 77 to 79 AD, which covers astronomy, geography, humans and their technology, medicine, and superstition, as well as animals and plants.

Medieval European academics considered knowledge to have two main divisions: the humanities (primarily what is now known as classics) and divinity, with science studied largely through texts rather than observation or experiment. The study of nature revived in the Renaissance, and quickly became a third branch of academic knowledge, itself divided into descriptive natural history and natural philosophy, the analytical study of nature. In modern terms, natural philosophy roughly corresponded to modern physics and chemistry, while natural history included the biological and geological sciences. The two were strongly associated. During the heyday of the gentleman scientists, many people contributed to both fields, and early papers in both were commonly read at professional science society meetings such as the Royal Society and the French Academy of Sciences—both founded during the 17th century.

Natural history had been encouraged by practical motives, such as Linnaeus' aspiration to improve the economic condition of Sweden. Similarly, the Industrial Revolution prompted the development of geology to help find useful mineral deposits.

Modern definitions of natural history come from a variety of fields and sources, and many of the modern definitions emphasize a particular aspect of the field, creating a multiplicity of definitions with a number of common themes among them. For example, while natural history is most often defined as a type of observation and a subject of study, it can also be defined as a body of knowledge, and as a craft or a practice, in which the emphasis is placed more on the observer than on the observed. The multiplicity of definitions for the field has been recognized as both a weakness and a strength, and a broad range of definitions has recently been offered by practitioners in a recent collection of views on natural history.

Definitions from biologists often focus on the scientific study of individual organisms in their environment, as seen in this definition by Marston Bates: "Natural history is the study of animals and Plants—of organisms. ... I like to think, then, of natural history as the study of life at the level of the individual—of what plants and animals do, how they react to each other and their environment, how they are organized into larger groupings like populations and communities" and this more recent definition by D.S. Wilcove and T. Eisner: "The close observation of organisms—their origins, their evolution, their behavior, and their relationships with other species".