Brazil’s Atlantic Coast rainforest, or Mata Atlântica, harbours one of the highest numbers of species of any forest in the world. 1 Many hundreds of kilometres of arid and semi-arid country separate it from the Brazilian Amazon and about two-thirds of the plant and animal species that live in the Mata Atlântica are not native to the Amazon rainforest. Perhaps most remarkably, the Mata Atlântica still retains immense biodiversity comparable to that of any other terrestrial ecosystem in the world in spite of the fact that somewhere between 93 and 97 per cent of its forest is reported to have been destroyed over the last five centuries. One of the reasons it has been able to maintain such high diversity is that some, though not most, of the crops and cultivation techniques used in portions of the forest’s range are themselves compatible with high species diversity. In particular, plantations of shade-grown cacao have recently been discovered to have sheltered high levels of biodiversity even during those periods when the plantations were a major source of raw product for the world’s chocolate factories. The cacao-growing region has been designated by the International Union for the Conservation of Nature as one of the ten most important ‘hotspots’ for biodiversity conservation in the world because of the conjoined circumstances of enormously high and significant biodiversity and the powerful forces that could quickly destroy that diversity. How and why this came to be provides rich and complex insights into how agriculture can play a critical role in preserving biodiversity.