Extracorporeal membrane oxygenation (ECMO) has increasingly been used in patients with refractory severe cardiorespiratory failure in recent years. The use of ECMO necessitates anticoagulation as blood passes through an extracorporeal circuit that has a membrane lung and a centrifugal pump. Although heparin is the most common anticoagulant used during ECMO runs, other anticoagulants like direct thrombin inhibitors and Factor X inhibitors have also been implemented in special circumstances. Bleeding is a well-known and severe complication while receiving ECMO, and balancing this against circuit thrombosis is a clinical challenge. While standard laboratory tests, such as activated partial thromboplastin time and point-of-care tests such as activated clotting time, help monitor anticoagulation on ECMO, they have their drawbacks. The use of viscoelastic assays (VEAs) in aiding anticoagulation management on ECMO has shown some benefits in reducing bleeding and thrombotic complications, though these assays are not widely used at present. This article explores the challenges of monitoring anticoagulation on ECMO and reviews the available evidence regarding VEAs in adult and pediatric ECMO.