Oral squamous cell carcinoma progression depends on its carcinogenic mutation which gives this tumor the ability to infiltrate different types of tissue in the surroundings. Infiltration of muscles, nerves, blood, and lymphatic vessels occurs with different and not well-known pathophysiological mechanisms. These pathways of diffusion represent one of the most important issues in compartmental surgery. This chapter aims to clarify some of the instruments that the carcinogenic process uses in order to infiltrate the surrounding tissues. Understanding tumors’ pathways of invasion means understanding which structures are at risk and, for this reason, need to be removed in order to prevent local postoperative relapse.