Financial toxicity is a preventable cancer treatment side effect, encompassing the subjective financial distress and objective financial burden that result from increased spending and decreased earning after diagnosis. The prevalence of financial toxicity has increased with new expensive cancer treatments and insurers gradually shifting costs to patients. Patients with financial toxicity experience increased symptom burden, treatment nonadherence, and cancer-related death. The patients at highest risk are young, female, and nonwhite. For low-income patients, the indirect costs of cancer care can be especially burdensome and include child/elder care, transportation, unpaid work absences or job loss, cancer-related comorbidity treatment costs, and fulfilling dietary requirements. Psychosocial impacts include depression, emotional distress, and reduced quality of life. Patients in palliative care have rated financial distress as more severe than physical, familial, and emotional distress. Interventions and policy changes are needed to ameliorate the effects of financial toxicity, especially for the most vulnerable groups.