Many of the building blocks of life such as amino acids and nucleotides are chiral, i.e., different from their mirror image. Contemporary life selects and synthesizes only one of two possible handednesses. Chiral molecules also tend to be optically active and rotate polarized light in a left-handed sense for many proteins and in a right-handed sense for many nucleotides and sugars. In an abiotic environment, however, there are usually equally many left-and right-handed molecules, so we talk about a racemic mixture. If homochirality was a prerequisite of life, there must have been physical or chemical circumstances that led to the selection of a certain preference. Conversely, if it was a consequence of life, we must identify possible pathways for accomplishing a transition from a racemic to a homochiral chemistry. There has been significant progress on both approaches. One of the four elementary forces of nature, the weak force, responsible for the decay of free neutrons, for example, does give rise to a preference for chemical reactions between molecules of a certain chirality, but the effect is very small compared to that of random fluctuations that are always present. On the other hand, amino acids from certain meteorites suggest a preference for the left-handed amino acids -at least for some of them -although the question of contamination is not fully ruled out. This could be explained by polarized light, which can give rise to a selection of a net handedness of biomolecules, but the effect is again small. Depending on the mechanism that is responsible for generating polarized light, either both signs or only one sign of polarization are possible. After a detailed discussion of these ideas and the observational evidence, we