The year 1823 in science and technology involved some significant events, listed below.

• Olbers' paradox is described by the German astronomer Heinrich Wilhelm Matthäus Olbers.
• Cambridge Observatory established in England.^[1]
• December 29 – Great Comet of 1823 first observed.

• June 17 – Charles Macintosh patents a method of rubberizing fabric to waterproof it.^[2]

• February 20 – James Weddell's expedition to Antarctica reaches latitude 74°15' S and longitude 34°16'45" W, the most southerly position that will be attained for more than 80 years.

• János Bolyai completes a treatise on parallel lines that he calls absolute geometry, although it will not be published until 1832.

• After August – Philipp Franz von Siebold begins to introduce Western medicine to Japan.
• October 5 – The Lancet founded by Thomas Wakley.
• Theodric Romeyn Beck publishes the first significant American book on forensic medicine, Elements of Medical Jurisprudence in Albany, New York.

• January 23 – In a cave on the Gower Peninsula of Wales, William Buckland inspects the "Red Lady of Paviland", the first identification of a prehistoric (male) human burial. The bones, discovered on December 21 last, are with those of the woolly mammoth, proving that the two had coexisted.^[3]
• December 10 – On the Jurassic Coast of southern England, Mary Anning finds the first complete Plesiosaurus skeleton.^[4]

• William Sturgeon invents the electromagnet.

• December 6 – English inventor Samuel Brown obtains his first patent for a hydrogen fuelled compressionless atmospheric gas vacuum engine,^[5] the first internal combustion engine to be applied industrially.^[6]
• First use of a Fresnel lens in a lighthouse optic, at the Cordouan lighthouse on the Gironde estuary.^[7]
• First permanent wire cable suspension bridge, Pont Saint Antoine in Geneva, by Guillaume Henri Dufour, of two 40 m spans.^[8]
• First cast iron framed greenhouse erected at Wollaton Park in England as a Camellia house.
• French officer Henri-Joseph Paixhans develops the Paixhans gun, the first naval artillery to fire explosive shells.

• Annals of the New York Academy of Sciences first published.

• Copley Medal: John Pond^[9]

• January 3 – Robert Whitehead (died 1905), English inventor of the self-propelled torpedo.
• January 8 – Alfred Russel Wallace (died 1913), British naturalist who devises the theory of natural selection at the same time as Charles Darwin.
• February 3 – Spencer Fullerton Baird (died 1887), American ornithologist and ichthyologist.
• March 21 – Jules Émile Planchon (died 1888), French botanist.
• December 22 – Jean Henri Fabre (died 1915), French entomologist.
• December 23 – Thomas W. Evans (died 1897), American-born dentist.^[10]

• January 26 – Edward Jenner (born 1749), English inventor of vaccine.
• January 27 – Charles Hutton (born 1737), English mathematician.
• February 9 – Agnes Ibbetson (born 1757), English plant physiologist.
• September 23 – Matthew Baillie (born 1761), British pathologist.