Ultrasound has become indispensable in the management of patients supported with extracorporeal membrane oxygenation (ECMO), enabling rapid diagnosis, procedural guidance, physiologic monitoring, and informed decision-making across the entire ECMO continuum. This review, conducted under the auspices of the Extracorporeal Life Support Organization (ELSO), provides evidence-based recommendations for the use of ultrasound in adult, pediatric, and neonatal ECMO patients. An international, multidisciplinary panel of experts with dual expertise in ECMO and ultrasound, representing all ELSO chapters, convened to define the scope and structure of the review. A comprehensive literature review identified 133 relevant publications informing recommendations. The review addresses training and competency requirements, choice of ultrasound modalities, and the role of ultrasound before ECMO initiation, during cannulation, throughout ECMO support, for troubleshooting complications, and during ECMO weaning and post-decannulation care. Pre-ECMO ultrasound is emphasized for assessment of cardiopulmonary function, vascular anatomy, and identification of contraindications or reversible conditions. Real-time ultrasound guidance is recommended for cannulation to reduce complications and confirm optimal cannula positioning. During ECMO, echocardiography and extracardiac ultrasound are central to monitoring cardiac function, cannula position, ventricular loading conditions, pulmonary pathology, neurological complications, and vascular integrity. Ultrasound-based strategies for diagnosing hypoxemia, recirculation, tamponade, ventricular distension, and limb ischemia are detailed. Finally, ultrasound plays a critical role in assessing readiness for ECMO liberation and identifying post-ECMO complications. This review highlights the pervasive role of ultrasound as a core competency in ECMO care and provides a practical framework to support safe, effective, and standardized ultrasound use across diverse ECMO programs worldwide.