A geometer is a mathematician whose area of study is geometry.

Some notable geometers and their main fields of work, chronologically listed, are:

• Baudhayana (fl. c. 800 BC) – Euclidean geometry
• Manava (c. 750 BC–690 BC) – Euclidean geometry
• Thales of Miletus (c. 624 BC – c. 546 BC) – Euclidean geometry
• Pythagoras (c. 570 BC – c. 495 BC) – Euclidean geometry, Pythagorean theorem
• Zeno of Elea (c. 490 BC – c. 430 BC) – Euclidean geometry
• Hippocrates of Chios (born c. 470 – 410 BC) – first systematically organized Stoicheia – Elements (geometry textbook)
• Mozi (c. 468 BC – c. 391 BC)
• Plato (427–347 BC)
• Theaetetus (c. 417 BC – 369 BC)
• Autolycus of Pitane (360–c. 290 BC) – astronomy, spherical geometry
• Euclid (fl. 300 BC) – Elements, Euclidean geometry (sometimes called the "father of geometry")
• Apollonius of Perga (c. 262 BC – c. 190 BC) – Euclidean geometry, conic sections
• Archimedes (c. 287 BC – c. 212 BC) – Euclidean geometry
• Eratosthenes (c. 276 BC – c. 195/194 BC) – Euclidean geometry
• Katyayana (c. 3rd century BC) – Euclidean geometry

• Hero of Alexandria (c. AD 10–70) – Euclidean geometry
• Pappus of Alexandria (c. AD 290–c. 350) – Euclidean geometry, projective geometry
• Hypatia of Alexandria (c. AD 370–c. 415) – Euclidean geometry
• Brahmagupta (597–668) – Euclidean geometry, cyclic quadrilaterals
• Vergilius of Salzburg (c.700–784) – Irish bishop of Aghaboe, Ossory and later Salzburg, Austria; antipodes, and astronomy
• Al-Abbās ibn Said al-Jawharī (c. 800–c. 860)
• Thabit ibn Qurra (826–901) – analytic geometry, non-Euclidean geometry, conic sections
• Abu'l-Wáfa (940–998) – spherical geometry, spherical triangles
• Alhazen (965–c. 1040)
• Omar Khayyam (1048–1131) – algebraic geometry, conic sections
• Ibn Maḍāʾ (1116–1196)

• Piero della Francesca (1415–1492)
• Leonardo da Vinci (1452–1519) – Euclidean geometry
• Jyesthadeva (c. 1500 – c. 1610) – Euclidean geometry, cyclic quadrilaterals
• Marin Getaldić (1568–1626)
• Jacques-François Le Poivre (1652–1710), projective geometry
• Johannes Kepler (1571–1630) – (used geometric ideas in astronomical work)
• Edmund Gunter (1581–1686)
• Girard Desargues (1591–1661) – projective geometry; Desargues' theorem
• René Descartes (1596–1650) – invented the methodology of analytic geometry, also called Cartesian geometry after him
• Pierre de Fermat (1607–1665) – analytic geometry
• Blaise Pascal (1623–1662) – projective geometry
• Christiaan Huygens (1629–1695) – evolute
• Giordano Vitale (1633–1711)
• Philippe de La Hire (1640–1718) – projective geometry
• Isaac Newton (1642–1727) – 3rd-degree algebraic curve
• Giovanni Ceva (1647–1734) – Euclidean geometry
• Johann Jacob Heber (1666–1727) – surveyor and geometer
• Giovanni Gerolamo Saccheri (1667–1733) – non-Euclidean geometry
• Leonhard Euler (1707–1783)
• Tobias Mayer (1723–1762)
• Johann Heinrich Lambert (1728–1777) – non-Euclidean geometry
• Gaspard Monge (1746–1818) – descriptive geometry
• John Playfair (1748–1819) – Euclidean geometry
• Lazare Nicolas Marguerite Carnot (1753–1823) – projective geometry
• Joseph Diaz Gergonne (1771–1859) – projective geometry; Gergonne point
• Carl Friedrich Gauss (1777–1855) – Theorema Egregium
• Louis Poinsot (1777–1859)
• Siméon Denis Poisson (1781–1840)
• Jean-Victor Poncelet (1788–1867) – projective geometry
• Augustin-Louis Cauchy (1789–1857)
• August Ferdinand Möbius (1790–1868) – Euclidean geometry
• Nikolai Ivanovich Lobachevsky (1792–1856) – hyperbolic geometry, a non-Euclidean geometry
• Michel Chasles (1793–1880) – projective geometry
• Germinal Dandelin (1794–1847) – Dandelin spheres in conic sections
• Jakob Steiner (1796–1863) – champion of synthetic geometry methodology, projective geometry, Euclidean geometry

• Karl Wilhelm Feuerbach (1800–1834) – Euclidean geometry
• Julius Plücker (1801–1868)
• János Bolyai (1802–1860) – hyperbolic geometry, a non-Euclidean geometry
• Christian Heinrich von Nagel (1803–1882) – Euclidean geometry
• Johann Benedict Listing (1808–1882) – topology
• Hermann Günther Grassmann (1809–1877) – exterior algebra
• Ludwig Otto Hesse (1811–1874) – algebraic invariants and geometry
• Ludwig Schlafli (1814–1895) – Regular 4-polytope
• Pierre Ossian Bonnet (1819–1892) – differential geometry
• Arthur Cayley (1821–1895)
• Joseph Bertrand (1822–1900)
• Delfino Codazzi (1824–1873) – differential geometry
• Bernhard Riemann (1826–1866) – elliptic geometry (a non-Euclidean geometry) and Riemannian geometry
• Julius Wilhelm Richard Dedekind (1831–1916)
• Ludwig Burmester (1840–1927) – theory of linkages
• Edmund Hess (1843–1903)
• Albert Victor Bäcklund (1845–1922)
• Max Noether (1844–1921) – algebraic geometry
• Henri Brocard (1845–1922) – Brocard points
• William Kingdon Clifford (1845–1879) – geometric algebra
• Pieter Hendrik Schoute (1846–1923)
• Felix Klein (1849–1925)
• Sofia Vasilyevna Kovalevskaya (1850–1891)
• Evgraf Fedorov (1853–1919)
• Henri Poincaré (1854–1912)
• Luigi Bianchi (1856–1928) – differential geometry
• Alicia Boole Stott (1860–1940)
• Hermann Minkowski (1864–1909) – non-Euclidean geometry
• Henry Frederick Baker (1866–1956) – algebraic geometry
• Élie Cartan (1869–1951)
• Dmitri Egorov (1869–1931) – differential geometry
• Veniamin Kagan (1869–1953)
• Raoul Bricard (1870–1944) – descriptive geometry
• Ernst Steinitz (1871–1928) – Steinitz's theorem
• Marcel Grossmann (1878–1936)
• Oswald Veblen (1880–1960) – projective geometry, differential geometry
• Nathan Altshiller Court (1881–1968), author of College Geometry
• Emmy Noether (1882–1935) – algebraic topology
• Harry Clinton Gossard (1884–1954)
• Arthur Rosenthal (1887–1959)
• Helmut Hasse (1898–1979) – algebraic geometry

H. S. M. Coxeter	Ernst Witt	Benoit Mandelbrot
Branko Grünbaum	Michael Atiyah	J. H. Conway
William Thurston	Mikhail Gromov	George W. Hart
Shing-Tung Yau	Károly Bezdek	Grigori Perelman
Denis Auroux

• William Vallance Douglas Hodge (1903–1975)
• Patrick du Val (1903–1987)
• Beniamino Segre (1903–1977) – combinatorial geometry
• J. C. P. Miller (1906–1981)
• André Weil (1906–1998) – Algebraic geometry
• H. S. M. Coxeter (1907–2003) – theory of polytopes, non-Euclidean geometry, projective geometry
• J. A. Todd (1908–1994)
• Daniel Pedoe (1910–1998)
• Shiing-Shen Chern (1911–2004) – differential geometry
• Ernst Witt (1911–1991)
• Rafael Artzy (1912–2006)
• Aleksandr Danilovich Aleksandrov (1912–1999)
• László Fejes Tóth (1915–2005)
• Edwin Evariste Moise (1918–1998)
• Aleksei Pogorelov (1919–2002) – differential geometry
• Magnus Wenninger (1919–2017) – polyhedron models
• Jean-Louis Koszul (1921–2018)
• Isaak Yaglom (1921–1988)
• Eugenio Calabi (1923–2023)
• Benoit Mandelbrot (1924–2010) – fractal geometry
• Katsumi Nomizu (1924–2008) – affine differential geometry
• Michael S. Longuet-Higgins (1925–2016)
• John Leech (1926–1992)
• Alexander Grothendieck (1928–2014) – algebraic geometry
• Branko Grünbaum (1929–2018) – discrete geometry
• Michael Atiyah (1929–2019)
• Lev Semenovich Pontryagin (1908–1988)
• Geoffrey Colin Shephard (1927–2016)
• Norman W. Johnson (1930–2017)
• John Milnor (1931–)
• Roger Penrose (1931–)
• Yuri Manin (1937–2023) – algebraic geometry and diophantine geometry
• Vladimir Arnold (1937–2010) – algebraic geometry
• Ernest Vinberg (1937–2020)
• J. H. Conway (1937–2020) – sphere packing, recreational geometry
• Robin Hartshorne (1938–) – geometry, algebraic geometry
• Phillip Griffiths (1938–) – algebraic geometry, differential geometry
• Enrico Bombieri (1940–) – algebraic geometry
• Robert Williams (1942–)
• Peter McMullen (1942–)
• Richard S. Hamilton (1943–) – differential geometry, Ricci flow, Poincaré conjecture
• Mikhail Gromov (1943–)
• Rudy Rucker (1946–)
• William Thurston (1946–2012)
• Shing-Tung Yau (1949–)
• Michael Freedman (1951–)
• Egon Schulte (1955–) – polytopes
• George W. Hart (1955–) – sculptor
• Károly Bezdek (1955–) – discrete geometry, sphere packing, Euclidean geometry, non-Euclidean geometry
• Simon Donaldson (1957–)
• Kenji Fukaya (1959–) – symplectic geometry
• Oh Yong-Geun (1961–)
• Toshiyuki Kobayashi (1962–)
• Hiraku Nakajima (1962–) – representation theory and geometry
• Hwang Jun-Muk (1963–) – algebraic geometry, differential geometry
• Grigori Perelman (1966–) – Poincaré conjecture
• Maryam Mirzakhani (1977–2017)
• Denis Auroux (1977–)

• Mathematics and architecture