This research explores the application of carbon, nitrogen, oxygen and hydrogen isotopic analysis of modem human hair and nail tissues for forensic purposes. Carbon and nitrogen isotopic signatures are transferred from the environment to plants and to human tissues through trophic levels, therefore reflecting the diet. Oxygen and hydrogen isotopes are closely linked to the geographical location of the individuals through precipitation. drinking water and food products. The use of carbon, nitrogen, oxygen and hydrogen isotopic analysis of "hair and nail tissues can therefore be applied to diet-reconstruction and geo-localisation of individuals, which has been widely used on older human remains. Hair and nail are ideal tissues for obtaining a precise temporal archive of diet and location due to their known and relatively constant growth rates. The high keratin content of these tissues (between 65 and 95% by weight) enables analysis of small sample sizes, without prior chemical purification, which makes them ideal matrices in forensic investigations where sample size is often a limiting factor. The easy and non• invasive sampling of hair and nail tissues enables the transfer of this application to living humans, which has been the focus of forensic scientists for several years. In this study, hair and nail samples were collected from 134 volunteers from Reading (UK) with known diet and geographical movements. A total of 43 hair samples and 74 fingernail samples were also collected from volunteers living in Kenya, whose recent travel record was known. A total of 17 hair samples and 10 fingernail samples were also collected from a group of27 individuals claiming to be of Somalian origin but who could have been Kenyan, as part of the British Human Provenance Project. These samples were compared to the two reference groups from Reading and Kenyan volunteers in order to assess their likely area of origin, and to determine their diet. The results obtained in this study confirm the potential of carbon and nitrogen isotopic analysis of modem human hair and nail tissues in discriminating between the different levels of protein intake of omnivore, ovo-lacto-vegetarian (OL V) and vegan diets. Through the largest dataset analysed so far (mostly from Europe and Kenya), this research confidently reports the effect of location on δ13C, δ 2H and δ 180 values of human tissues. Hair and nail δ13C values show significant differences between locations with diverse proportion of C3/C4 food product intake (USA and Kenya versus Europe), while locations such as Kenya, Australia and Turkey show significantly enriched 02H and δ180 values than locations at higher latitudes such as Spain, France, Germany and the United-Kingdom. The level of location discrimination is however increased by a simultaneous combined approach of δJ3C and δ2H analysis, which enables the determination of the likely area of origin of samples from uncertain location to a greater extent than the isotope ratio pairs (δ13C- δ15N, δ2H- δ18O). This study also presents a unique dataset of a series of hair and nail samples from the same individual (n=74 for δ13C and δ 15N and n=60 for δ 2H and δ 18O), showing strong correlations between these two tissues.