It is universally agreed that a catastrophic loss of plant genetic diversity is occurring. Some species and, perhaps more importantly, gene combinations are being lost for perpetuity. Following the signing of the Biodiversity Convention in Rio there is even more awareness of the need to conserve the world's biodiversity. In recent years for various scientific and political reasons, the practical application of conservation has switched away from ex situ toward in situ techniques, i.e. the maintenance of germplasm in its natural wild habitat or within traditional agricultural systems. This text aims to provide a practical and theoretical introduction to the technique of in situ genetic conservation.