Conservation and enhancement of biodiversity are mentioned in the International Federation of Organic Agriculture Movements (IFOAM) standards and in all national guidelines as essential pillars for organic agriculture. Recent reviews show that organic agriculture enhances the number of species and the abundance of many taxa (plants, birds, mammals, earthworms, arthropods, soil microbes), compared with conventional agriculture. Considering the benefits for sustainability, a multi-criteria analysis shows that organic agriculture not only improves biodiversity but also has positive effects on soil (e.g., soil erosion, structure, biological activity), water (e.g., no pesticide residues) and climatic factors (e.g., air pollution). In organic horticulture, floral and faunal biodiversity fulfils important ecosystem services: it (i) reduces soil erosion; (ii) improves pollination of crops; and (iii) is an important component of pest management (i.e., conservation biocontrol). Therefore, conservation biocontrol is incorporated in a phased approach for arthropod pest management in organic horticulture. Together with suitable cultural practices, the enhancement of soil quality, the choice of resistant cultivars and the implementation of functional biodiversity (e.g., incorporation of non-crop habitats such as hedgerows and wild flower strips) help to prevent pest outbreaks. If these indirect measures do not provide sufficient pest control the programme includes deployment of direct measures such as biocontrol agents and approved insecticides, repellents, and pheromones. The biodiversity aspects of sustainability and pest management in organic systems are highlighted by presenting results of recent reviews and case studies in organic horticulture.