Necrotizing soft tissue infections (NSTIs) are severe infections that destroy skin and underlying tissue and are often caused by the bacterium Streptococcus pyogenes. In this EU-funded project, INFECT, the aim is to define host and bacterial derived components that contribute to the pathogenesis of NSTIs. Using an organotypic model of human skin, we explore host and bacterial-derived components that contribute to the pathogenesis at the local site of infection. The skin tissue model was exposed to different Group A streptococci isolates collected from NSTI patients enrolled in INFECT. Histological and immunofluorescence analyses of infected tissue models revealed structural damage of the stratified epithelial cell layer, and underlying tissue. Gram staining of the infected model tissue revealed bacterial dissemination throughout the entire tissue at 24h to 48h after infection. Analysis of tissue model supernatants revealed increasing IL-1β levels over the infection period, confirming results obtained in patients and a murine model of NSTIs. The further analysis of infected skin tissue models revealed the capability of GAS isolates to form biofilm, allowing studies on the requirements for biofilm formation in NSTIs. The human organotypic skin model has been further developed, involving studies on the role of macrophages and adipocytes in NSTIs. In summary, exploitation of the human organotypic skin model provides a novel powerful tool to study the pathogenesis of NSTIs and has contributed to the identification of IL1β as a potential key regulator in NSTIs, and biofilm to be considered as a potential complicating microbiological feature of GAS NSTI.