Tatyana Alexeyevna Afanasyeva (Russian: Татья́на Алексе́евна Афана́сьева) (Kiev, 19 November 1876 – Leiden, 14 April 1964) (also known as Tatiana Ehrenfest-Afanaseva or spelled Afanassjewa) was a Russian-Dutch mathematician and physicist who made contributions to the fields of statistical mechanics and statistical thermodynamics.[1] On 21 December 1904, she married Austrian physicist Paul Ehrenfest (1880–1933). They had two daughters and two sons; one daughter, Tatyana Ehrenfest, also became a mathematician.