The assessment of nanoparticle penetration through skin is of increasing importance not only to evaluate the toxicity associated with occupational or environmental exposure to nanoparticles, but also to design rules for the fabrication of new types of transdermal drug delivery or diagnostics approaches. While these have been the subject of much research, the lack of a systematic approach in the penetration experiments has created controversial results regarding whether nanoparticles do or not penetrate the skin. The aim of the research presented in the thesis is to investigate the penetration of gold nanoparticles through human and mouse skin, focusing on the effect of surface charge, morphology and specific functionalisation. To study this, a penetration protocol using organ culture was designed and tested to assure the maintenance of the skin integrity in the course of our experiments. Skin samples incubated with gold nanoparticles were characterized for penetration by NPs using inductively coupled plasma atomic emission spectroscopy, transmission electron microscopy, energy-dispersive Xray spectroscopy and photoluminescence microscopy. Furthermore, epithelial cell monolayers were exposed to the gold nanoparticles to evaluate the transport through the cellular barrier. Transmission electron microscopy, light microscopy and trans epithelial electric resistance were used to characterise the cell monolayers exposed to gold nanoparticles. Results obtained are important to enhance our understanding of the interaction of gold nanoparticles with skin, providing valuable information for the design of new nanoparticle-based transdermal delivery systems.