This chapter concerns the use of flowering plants in organic agroecosystems. First, a review of the available literature explores the use of flower strips in controlling pest populations as part of conservation biological control. The positive effects of flower strips on beneficial insects are then explored and potential candidates for flower strips proposed. Finally, practical recommendations for installing flower strips are given. Secondly, a case study is presented: The use of flowering plants in organic mango orchards in Reunion. We study the interactions between selected flowering plants and beneficial and pest arthropods. We initially focus on all arthropods and we characterize the insect fauna present on three selected plants. We then focus on the entomological group Parasitica (Hymenoptera), many of which are parasitoids of other insects, including pests. The plant with the greatest abundance and diversity of Parasitica is Lobularia maritima (Brassicaceae). In 2013, we used malaise traps to ascertain that an orchard containing flower strips harbors 10 times more parasitoids than a bare orchard. These results confirm the value of using flowering plants as a conservation biological control tool to encourage pest parasitoids in organic farming.