The number of patients with adult congenital heart disease (ACHD) has been dramatically increasing and adults with congenital heart disease now outnumber children with congenital heart disease. However, patients with ACHD are still at increased risk of morbidity and mortality due to residua and sequelae. Although echocardiography is an indispensable imaging modality in the comprehensive assessment of ACHD, accurate echocardiographic assessment of ACHD is challenging especially for physicians or sonographers who are not familiar with ACHD because of its complex morphology, physiology, and hemodynamics. A recently developed fusion imaging technology can provide synchronized display of real-time echocardiographic images and multiplanar reconstruction images of computed tomography or magnetic resonance imaging corresponding to the image plane of real-time echocardiography. We have reported the clinical utility of this fusion imaging technology for the precise evaluation of complex ACHD. On the other hand, conventional echocardiographic technology also plays an important role in assessing unique ACHD pathophysiology. For example, restrictive right ventricular physiology is a common finding after tetralogy of Fallot or pulmonary stenosis repair and can be evaluated by conventional pulsed-wave Doppler. In this review, we discuss the clinical usefulness of modern and conventional echocardiographic technologies for the evaluation of ACHD by presenting a case series.