孟德尔定律是一系列描述了生物特性的遗传规律并催生了遗传学诞生的著名定律，包括两项基本定律和一项原则即：显性原则、分离定律（孟德尔第一定律），以及自由组合定律（孟德尔第二定律）。此定律由奥地利修道院士格里哥·孟德尔于1865至1866年间发表，并在1900年被重新发现。定律发表初时颇具争议。孟德尔定律与托马斯·摩尔根1915年发表的遗传的染色体学说（英语：Boveri-Sutton chromosome theory）共同组成了经典遗传学的基础。英国遗传学家罗纳德·费希尔将二者与自然选择学说相结合，发表于他1930年的著作《自然选择的遗传理论》（英语：The Genetical Theory of Natural Selection）中，他为进化提供了数学理论基础，同时也是群体遗传学和现代演化综论的奠基者。

Mendelian inheritance is inheritance of biological features that follows the laws proposed by Gregor Johann Mendel in 1865 and 1866 and re-discovered in 1900. It was initially very controversial. When Mendel's theories were integrated with the Boveri–Sutton chromosome theory of inheritance by Thomas Hunt Morgan in 1915, they became the core of classical genetics while Ronald Fisher combined them with the theory of natural selection in his 1930 book The Genetical Theory of Natural Selection, putting evolution onto a mathematical footing and forming the basis for Population genetics and the modern evolutionary synthesis.