The increasing number of patients with adult congenital heart disease (ACHD) calls for the development of noninvasive imaging techniques that allow a long-term evaluation of native and postsurgical anatomy and function. Echocardiography remains the imaging modality of choice for congenital heart disease, but it is affected by limited acoustic windows and poor tissue characterization. Cardiac computed tomography and cardiac catheter angiography are 2 valid alternatives for the anatomic and functional assessment of ACHD; however, both use ionizing radiation, and cardiac catheter angiography requires an invasive approach. Cardiac magnetic resonance (CMR), noninvasively and in the absence of ionizing radiation, has the ability to evaluate the biventricular function, quantify flows, characterize tissue, and provide information on cardiac anatomy. Despite the long acquisition time and lower spatial resolution compared with cardiac computed tomography, CMR represents the ideal technique for long-term follow-up of ACHD. CMR is now widely utilized and is well described in the literature with regard to diagnosis, identification of complications, timing of surgery, and postoperative prognosis in ACHD. CMR represents a fundamental technique for the evaluation of patients with ACHD.