Informal/family caregivers are a fundamental source of care for cancer patients in the United States, yet the population of caregivers, their tasks, psychosocial needs and health outcomes are not well understood. Changes in the nature of cancer care and its delivery, along with the growing population of survivors and by consequence, their caregivers, warrant increased attention to the roles and demands of caregiving. This paper reviews current evidence presented in a two-day meeting to examine the state of the science of informal cancer caregiving convened by the National Cancer Institute and National Institute for Nursing Research. The meeting sought to define who is an informal cancer caregiver, summarize the state of the science in informal cancer caregiving, and describe both the kinds of interventions developed to address caregiving challenges and the various outcomes used to evaluate their impact. This paper offers recommendations for moving science forward in four areas: (1) improve estimation of the prevalence and burden of informal cancer caregiving; (2) advance development of interventions designed to improve outcomes in cancer patients, caregivers, and patient-caregiver dyads; (3) generate and test strategies to integrate caregivers into formal healthcare settings; and (4) promote use of technology to support informal cancer caregivers.