The year 1811 in science and technology involved some significant events, listed below.

• March 25 – Great Comet discovered by Honoré Flaugergues.

• Johann Karl Wilhelm Illiger publishes Prodromus systematis mammalium et avium, an updating of Linnean taxonomy and a major influence on the concept of the 'Family' in biology. He first defines the infraclass Marsupialia.
• Peter Simon Pallas begins publication of Zoographia rosso-Asiatica, sistens omnium animalium in extenso Imperio rossico, et adjacentibus maribus observatorum recensionem, domicilia, mores et descriptiones, anatomen atque icones plurimorum in Saint Petersburg.

• Bernard Courtois discovers iodine.^[1]
• Joseph Louis Gay-Lussac and Louis Jacques Thénard publish Recherches Physico-Chimiques, faites sur la pile; sur la préparation chimique et les propriétés du potassium et du sodium; sur la décomposition de l'acide boracique; sur les acides fluorique, muriatique et muriatique oxigéné; sur l'action chimique de la lumière; sur l'analyse végétale et animale, etc. in Paris.
• Amedeo Avogadro proposes Avogadro's law, that equal volumes of gases under constant temperature and pressure contain equal number of molecules.^[2]

• June 10 – A volcanic eruption, observed from British sloop HMS Sabrina (1806), briefly creates Sabrina Island (Azores).

• Carl Friedrich Gauss works with functions of complex number variables.^[3]
• S. D. Poisson publishes Traité de mécanique (vol. 1).

• Charles Bell publishes An Idea of a New Anatomy of the Brain,^[4] starting to distinguish between sensory and motor nerves.
• Abraham Colles publishes A Treatise on Surgical Anatomy in Dublin.
• Francis Place publishes Illustrations and Proofs of the Principles of Population, including an examination of the proposed remedies of Mr. Malthus, and a reply to the objections of Mr. Godwin and others in London, the first significant text in English to advocate contraception.^[5]

• Mary Anning discovers the fossilised remains of an Ichthyosaur at Lyme Regis.

• Amedeo Avogadro proposes his hypothesis relating volumes and numbers of molecules of gases.

• Friedrich Koenig, with the assistance of Andreas Friedrich Bauer, produces the first steam rotary printing press, in London.^[6]

• Copley Medal: Benjamin Brodie^[7]

• March 2 – Hugh Edwin Strickland, English geologist and ornithologist (died 1853)
• March 11
  • Lady Katherine Sophia Kane née Baily, Irish botanist (died 1886)
  • Urbain Le Verrier, French astronomer (died 1877)
• March 30 – Robert Bunsen, German chemist (died 1899)
• July 13 – James Young, Scottish chemist (died 1883)
• September 14 – William Budd, English physician and epidemiologist (died 1880)
• October 25 – Évariste Galois, French mathematician (died 1832)
• John Waterston, Scottish physicist and civil engineer (died 1883)

• February 9 – Nevil Maskelyne, English Astronomer Royal (born 1732)
• August 31 – Louis Antoine de Bougainville, French explorer (born 1729)
• September 8 – Peter Simon Pallas, German-born naturalist (born 1741)