In this chapter, we will review the applications of point-of-care ultrasonography (POCUS) most pertinent to the care of the oncologic patient. Preexisting patient comorbidities combined with the local and systemic effects of cancer and its treatment can create a complex clinical picture with a broad differential diagnosis. POCUS can be rapidly deployed at the bedside to narrow the differential diagnosis and avoid significant delays in treatment for many conditions. The foundation of ultrasonography is a practical understanding of ultrasound physics, equipment, and artifacts. Cardiac POCUS and venous excess ultrasound (VExUS) can help guide the resuscitation of the hemodynamically unstable patient. Lung sonography can suggest the etiology of the dyspnea and guide weaning from mechanical ventilation. Routine use of POCUS can guide the management of many other conditions, including intracranial hypertension, venous thromboembolism, oliguria, and acute kidney injury. Despite the potential of POCUS, it is important to remember that guided training, routine application, and continuing education are requisites to deliver high-quality patient care and avoid iatrogenic injury.