This chapter explains the fundamental aspects of decontamination and sterilisation. A working knowledge of the principles of sterilisation, disinfection, and infection control are essential for effective and safe perioperative practice. Decontamination is defined as the combination of methods—including cleaning, disinfection, and sterilisation—used to make a reusable item safe for further use on patients and for handling by staff. The term refers to the whole cycle, including processes such as cleaning, disinfection, and sterilisation. Aseptic techniques are fundamental to supporting a safe environment and to ensure patient and staff safety with regards to infection and its associated risks. It is essential that perioperative practitioners adhere to national and local standards and understand how the decontamination cycle can mitigate the risk of infection.