In the late twentieth century, it was increasingly recognized that up to three-quarters of all patients who suffer an in-hospital cardiac arrest and/or require rescue transfer to a higher level of care have worsening physiological parameters in the antecedent hours prior to critical demise. This recognition highlighted the need for early identification of these patients to facilitate timely intervention and provide the appropriate language for escalation of care. Subsequent development and implementation of Early Warning Systems became a global healthcare initiative, and while there are multiple derivations, the vast majority of hospitals now utilize some form of track and trigger system to facilitate early identification of patients at risk of clinical demise. Oncology patients are at risk of clinical deterioration due to the neoplastic state, complications of antitumor therapies, and noncancer-related comorbidities. Early identification of at-risk oncology patients would prove particularly beneficial to facilitate early and appropriate discussions for treatment goals, ceilings of therapy, and multidisciplinary team input. At present, generic Early Warning Systems have not been validated in this population and fail to account for a persistent deranged physiology which may represent a new baseline in these patients. In this chapter we discuss the fundamental principles of Early Warning Systems and their position within modern medicine, their strengths and limitations, the associated infrastructures, and the particular challenges facing Early Warning Systems in oncological patients.