The homochirality of biological molecules is one of the basic mysteries of biogenesis. The predominance of l-amino acids and d-hydrocarbons in living matter stands in contrast to the chemical principle of symmetry between enantiomers. An answer to the puzzle needs to include a plausible explanation of how the natural racemic balance was initially tipped in favor of one enantiomer and how the initial tiny excess was amplified to significant levels. It is also necessary to consider how the imbalance was sustained from returning to a thermodynamic equilibrium. This is a review of the main concepts and observations, followed by a brief discussion.