Organic farming, also known as organic agriculture or ecological farming or biological farming, is an agricultural system that emphasizes the use of naturally occurring, non-synthetic inputs, such as compost manure, green manure, and bone meal and places emphasis on techniques such as crop rotation, companion planting, and mixed cropping. Biological pest control methods such as the fostering of insect predators are also encouraged. Organic agriculture can be defined as "an integrated farming system that strives for sustainability, the enhancement of soil fertility and biological diversity while, with rare exceptions, prohibiting synthetic pesticides, antibiotics, synthetic fertilizers, genetically modified organisms, and growth hormones". It originated early in the 20th century in reaction to rapidly changing farming practices. Certified organic agriculture accounted for 70 million hectares (170 million acres) globally in 2019, with over half of that total in Australia.

Organic standards are designed to allow the use of naturally occurring substances while prohibiting or severely limiting synthetic substances. For instance, naturally occurring pesticides, such as garlic extract, bicarbonate of soda, or pyrethrin (which is found naturally in the Chrysanthemum flower), are permitted, while synthetic fertilizers and pesticides, such as glyphosate, are prohibited. Synthetic substances that are allowed only in exceptional circumstances may include copper sulfate, elemental sulfur, and veterinary drugs. Genetically modified organisms, nanomaterials, human sewage sludge, plant growth regulators, hormones, and antibiotic use in livestock husbandry are prohibited. Broadly, organic agriculture is based on the principles of health, care for all living beings and the environment, ecology, and fairness. Organic methods champion sustainability, self-sufficiency, autonomy and independence, health, animal welfare, food security, and food safety. It is often seen as part of the solution to the impacts of climate change.

Organic agricultural methods are internationally regulated and legally enforced by transnational organizations such as the European Union and also by individual nations, based in large part on the standards set by the International Federation of Organic Agriculture Movements (IFOAM), an international umbrella organization for organic farming organizations established in 1972, with regional branches such as IFOAM Organics Europe and IFOAM Asia. Since 1990, the market for organic food and other products has grown rapidly, reaching $150 billion worldwide in 2022 – of which more than $64 billion was earned in North America and EUR 53 billion in Europe. This demand has driven a similar increase in organically managed farmland, which grew by 26.6 percent from 2021 to 2022. As of 2022, organic farming is practiced in 188 countries and approximately 96,000,000 hectares (240,000,000 acres) worldwide were farmed organically by 4.5 million farmers, representing approximately 2 percent of total world farmland.

Organic farming can be beneficial on biodiversity and environmental protection at local level; however, because organic farming can produce lower yields compared to intensive farming, leading to increased pressure to convert more non-agricultural land to agricultural use in order to produce similar yields, it can cause loss of biodiversity and negative climate effects.

Agriculture was practiced for thousands of years without the use of artificial chemicals. Artificial fertilizers were first developed during the mid-19th century. These early fertilizers were cheap, powerful, and easy to transport in bulk. Similar advances occurred in chemical pesticides in the 1940s, leading to the decade being referred to as the "pesticide era". These new agricultural techniques, while beneficial in the short-term, had serious longer-term side-effects, such as soil compaction, erosion, and declines in overall soil fertility, along with health concerns about toxic chemicals entering the food supply. In the late 1800s and early 1900s, soil biology scientists began to seek ways to remedy these side effects while still maintaining higher production.

In 1921 the founder and pioneer of the organic movement, Albert Howard, and his wife Gabrielle Howard accomplished botanists, founded an Institute of Plant Industry to improve traditional farming methods in India. Among other things, they brought improved implements and improved animal husbandry methods from their scientific training; then by incorporating aspects of Indian traditional methods, developed protocols for the rotation of crops, erosion prevention techniques, and the systematic use of composts and manures. Stimulated by these experiences of traditional farming, when Albert Howard returned to Britain in the early 1930s he began to promulgate a system of organic agriculture.

In 1924 Rudolf Steiner gave a series of eight lectures on agriculture with a focus on influences of the moon, planets, non-physical beings and elemental forces. They were held in response to a request by adherent farmers who noticed degraded soil conditions and a deterioration in the health and quality of crops and livestock resulting from the use of chemical fertilizers. The lectures were published in November 1924; the first English translation appeared in 1928 as The Agriculture Course.

In July 1939, Ehrenfried Pfeiffer, the author of the standard work on biodynamic agriculture (Bio-Dynamic Farming and Gardening), came to the UK at the invitation of Walter James, 4th Baron Northbourne as a presenter at the Betteshanger Summer School and Conference on Biodynamic Farming at Northbourne's farm in Kent. One of the chief purposes of the conference was to bring together the proponents of various approaches to organic agriculture in order that they might cooperate within a larger movement. Howard attended the conference, where he met Pfeiffer. In the following year, Northbourne published his manifesto of organic farming, Look to the Land, in which he coined the term "organic farming". The Betteshanger conference has been described as the 'missing link' between biodynamic agriculture and other forms of organic farming.