After years of decline, resulting in the extinction of the sand lizard Lacerta agilis in Wales, the species has now been returned to several dune system sites which also contain the viviparous lizard Zootoca vivipara. As dune system habitats are becoming an increasingly important habitat type in the UK for L. agilis, providing a relatively safe haven for these and Z. vivipara populations from anthropogenic change, it is time to ensure the long-term survival of these populations. In this study, environmentally advantageous conditions for detection of both species were established for three dune system sites in North-West Wales. Surface temperature, UV, cloud cover and wind speed were identified as being the most influential detection parameters, with cloud cover and wind speed noted as having a negative influence on detection. Furthermore, favoured habitat was identified and ‘suitable habitat’ modelled for both species. Across the research sites both species were found to utilise habitats of a similar composition with reintroduced L. agilis favouring specific habitat features such as basking direction and degree of angle of their basking position. Habitat and site utilisation models indicate that for highly mobile dune systems L. agilis dispersal across a site is not of concern. For static or eroding dune systems, large, connected areas of favoured habitats are absent. In this situation, L. agilis dispersal (from introduction locations) is limited. Mean yearly L. agilis dispersal distances of 19.64 m – 28 m represents an approximate trend across the three research sites. The physical presence of L. agilis alone, however, does not constitute a successful reintroduction. Genetic diversity of the reintroduced populations was observed to be lower than those calculated in naturally occurring British populations. This is a matter of conservation concern, with a number of targeted mitigatory measures proposed to improve the genetic integrity, reducing the chance of population extinction(s). Mean time to extinction estimates indicate that for populations on highly mobile dune systems population survival times of between 11.4 yrs and 63.1 yrs could be expected. This is reduced for static or eroding dune system sites. The implications of these findings for the conservation of L. agilis and Z. vivipara are discussed in the context of current challenges and future management requirements. It is hoped that this thesis will help guide the future development of the reintroduction program, and in addition, provide a sound scientific basis for the future management of reintroduction sites and species monitoring.