The Zone System is a photographic technique for determining optimal film exposure and development, formulated by Ansel Adams and Fred Archer. Adams described how the Zone System was developed: "I take this opportunity to restate that the Zone System is not an invention of mine; it is a codification of the principles of sensitometry, worked out by Fred Archer and myself at the Art Center School in Los Angeles, around 1939-40."

The technique is based on the late 19th century sensitometry studies of Hurter and Driffield. The Zone System provides photographers with a systematic method of precisely defining the relationship between the way they visualize the photographic subject and the final results. Although it originated with black-and-white sheet film, the Zone System is also applicable to roll film, both black-and-white and color, negative and reversal, and to digital photography.

An expressive image involves the arrangement and rendering of various scene elements according to photographer’s desire. Achieving the desired image involves image management (placement of the camera, choice of lens, and possibly the use of camera movements) and control of image values. The Zone System is concerned with control of image values, ensuring that light and dark values are rendered as desired. Anticipation of the final result before making the exposure is known as visualization.

Ansel Easton Adams (February 20, 1902 – April 22, 1984) was an American photographer and environmentalist, best known for his black-and-white photographs of the American West, especially in Yosemite National Park.

With Fred Archer, Adams developed the Zone System as a way to determine proper exposure and adjust the contrast of the final print. The resulting clarity and depth characterized his photographs and the work of those to whom he taught the system. Adams primarily used large-format cameras despite their size, weight, setup time, and film cost, because their high resolution helped ensure sharpness in his images.

Adams founded the Group f/64 along with fellow photographers Willard Van Dyke and Edward Weston. Adams's photographs are reproduced on calendars, posters, and in books, making his photographs widely distributed.

Adams was born in the Western Addition of San Francisco, California, to distinctly upper-class parents Charles Hitchcock Adams and Olive Bray Adams. He was an only child and was named after his uncle Ansel Easton. His mother's family came from Baltimore and his maternal grandfather had a successful freight-hauling business, but squandered his wealth in failed mining and real estate ventures in Nevada. The Adams family came from New England, having migrated from the north of Ireland in the early 18th century. His grandfather founded and built a prosperous lumber business, which his father later ran, though his father's natural talents lay more with sciences than with business. Later in life, Adams would condemn that very same industry for cutting down many of the great redwood forests.

In the visual arts, color theory is a body of practical guidance to color mixing and the visual impacts of specific color combination. There are also definitions (or categories) of colors based on the color wheel: primary color, secondary color and tertiary color. Although color theory principles first appeared in the writings of Leone Battista Alberti (c.1435) and the notebooks of Leonardo da Vinci (c.1490), a tradition of "colory theory" began in the 18th century, initially within a partisan controversy around Isaac Newton's theory of color (Opticks, 1704) and the nature of so-called primary colors. From there it developed as an independent artistic tradition with only superficial reference to colorimetry and vision science.

The foundations of pre-20th-century color theory were built around "pure" or ideal colors, characterized by sensory experiences rather than attributes of the physical world. This has led to a number of inaccuracies in traditional color theory principles that are not always remedied in modern formulations.^{[citation needed]}