<p>The advent of graphene and more recently two-dimensional materials has opened new perspectives in electronics optoelectronics energy harvesting and sensing applications. This book based on a Special Issue published in Nanomaterials - MDPI covers experimental simulation and theoretical research on 2D materials and their van der Waals heterojunctions. The emphasis is the physical properties and the applications of 2D materials in state-of-the-art sensors and electronic or optoelectronic devices.</p>