Improvements in survival among cancer patients have revealed the clinical impact of cardiotoxicity on both cardiovascular and hematological and oncological outcomes, especially when it leads to the interruption of highly effective antitumor therapies. Atrial fibrillation is a common complication in patients with active cancer and its treatment poses a major challenge. These patients have an increased thromboembolic and hemorrhagic risk but standard stroke prediction scores have not been validated in this population. The aim of this expert consensus-based document is to provide a multidisciplinary and practical approach to the prevention and treatment of atrial fibrillation in patients with active cancer. This is a position paper of the Spanish Cardio-Oncology working group and the Spanish Thrombosis working group, drafted in collaboration with experts from the Spanish Society of Cardiology, the Spanish Society of Medical Oncology, the Spanish Society of Radiation Oncology, and the Spanish Society of Hematology.