In physics, recombination is the capture of an electron by a positive ion. It is the opposite process to ionization. As the electron drops through the energy levels of the atom with which it has recombined, it gives rise to emission lines that are known as recombination lines at specific wavelengths.

In genetics, recombination is the presence in offspring of gene combinations not found in either parent. Such new combinations may be formed by the crossing over of chromosomes in meiosis, and, being thus present in either gamete, unite randomly at fertilization.