Purpose of Review While left main coronary artery (LMCA) disease is often evaluated based on angiographic findings, technical limitations of angiography or the presence of intermediate disease can make accurate lesion assessment difficult. Recent Findings The rise of intravascular imaging and functional assessment of coronary artery disease lesions over the past 20 years has greatly improved PCI outcomes, making it an acceptal alternative to CABG in selected patients and lesions (Class IIa recommendation, after multidisciplinary Heart-Team discussion). We reviewed the advances of intravascular imaging (IVUS and OCT) and functional assessment (FFR and iFR) over the last 5-10 years specifically as it pertains to left main coronary artery disease. Functional assessment of the left main coronary artery and its bifurcations can help decide which lesion needs intervention. Summary Intravascular imaging prior to and after PCI of lesions involving the left main and its bifurcations leads to decreased frequency of PCI complications, and more importantly, better long-term outcomes for the patient owing to a decreased frequency of target-vessel and target-lesion revascularization. Keywords Left main • PCI • IVUS • FFR • Coronary artery disease • Intravascular imaging • Intermediate lesion assessmentThis article is part of the Topical Collection on Intravascular Imaging