This study details the breeding biology of the Malagasy radiated tortoise (Astrochelys radiata). Two tortoise populations were surveyed and compared considering their reproductive output. The influence of different living conditions and general reproduction characteristics of A. radiata are presented. The survival of A. radiata is currently threatened by the destruction of their natural habitat as a result of forest fragmentation and deforestation. In addition the tortoise species faces threats from poaching activities. Radiated tortoises are available on local markets for consumption and in the international pet trade. Trading bans such as CITES are largely ignored. Especially large females are collected in the wild as they may carry eggs which can also be consumed. Selective poaching may influence the reproduction of A. radiata by reducing the reproductive output of wild populations under the condition that reproductive success increases with age and size of the females. Therefore the relevance of large females for the reproductive output was analysed within this study. In this study clutch data and hatchlings from two different populations A. radiata were examined: (1) 40 female tortoises were observed in the Village des Tortues, Ifaty-Mangily, a tortoise rescue centre for animals that were detected in poaching attempts. The tortoises were held in enclosures where they were exposed to the biotic and abiotic conditions of their natural range. The animals received food and water on a regular basis. Surveys were conducted from February 2008 to June 2010 to observe the breeding activities. (2) A wild population of 25 female A. radiata were surveyed in the National Park Tsimanampetsotsa. The wild tortoises were equipped with radio-transmitters and surveyed from February to June in 2009 and 2010. Nine tortoises were observed during both survey years. The movement patterns of tortoises in the National Park were analysed in the context of local weather data and compared between survey years. Female body mass and egg mass were positively correlated as well as egg size and the offsprings’ carapace length. The reproductive output increased with availability of nutrition: tortoises of equal body mass from both populations were significantly more productive in captivity where they produced larger eggs and were able to lay several nests within a breeding season. The breeding behaviour in captivity stayed clearly seasonal. Egg deposition occurred between February and October and hatching was observed in December and January. The hatchlings of both populations showed no differences in body mass or size. However, hatching rates in the wild were three times higher than in captivity. A. radiata was observed to be more active during rainy days: radio-tagged individuals covered significantly longer distances compared to a drought period. All tortoises tracked within both survey years showed a distinct site fidelity: the home ranges of both years overlapped considerably. In consequence of selective poaching the tortoises in captivity were significantly larger than the individuals surveyed in the wild. Larger tortoises laid larger eggs which then produced larger hatchlings that presumably profit from increased chances of survival. Therefore large females are of major importance for the reproductive output of wild tortoise populations. However, the hatching success in the wild population was significantly higher than in captivity which may result from an unbalanced diet and limited space in the enclosures causing stressful living conditions in the captive population. Up to now the radiated tortoise was protected by a fady (Taboo) from trading or consumption. Fadys seem to be of major importance for nature conservation in Madagascar: they origin from traditional stories and find a wide acceptance among the local population. However, with migrating people from other parts of Madagascar, the protection by the ancestral taboo is weakening. Along its range A. radiata is collected by poachers and local tortoise populations are threatened by extinction. The removal of single individuals may already have a negative effect on wild tortoise populations. By selectively collecting large tortoises, in particular large females, the reproductive output of wild populations decreases: those animals with the greatest reproductive potential are removed from the wild. The radiated tortoise is still found in large numbers along it’s core range area. However, human influence on tortoise populations has to change significantly to keep A. radiata from extinction.