Molecular electronics, an emerging research field at the border of physics, chemistry, and material sciences, has attracted great interest in the last decade. To achieve the ultimate goal of designing molecular electronic devices with the desired functionality and experimental manipulation at the single-molecule level, theoretical understanding of electron transport at the nanoscale is an important prerequisite. This book, a multi-authored volume comprising reviews written by leading scientists, discusses recent advances in the field. It emphasizes the need for studies beyond the low-bias regime, a fact on which the scientific community became aware in the last years. To make the book useful for scientists of various disciplines interested in "learning by doing," each chapter is written in a science/tutorial hybrid style, with its own introduction presenting fundamental concepts and frameworks. The content reflects the strong transdisciplinary efforts needed for substantial progress.