In geometric knot theory, a central issue is to study the various geometric properties of knots when the knots have certain thickness. This setting makes a knot more like one that is tied with a uniform physical rope. These problems are mostly motivated by the recent applications of knot theory in fields such as biology and polymer chemistry. In this book, the authors first give a brief review of the basic concepts and terminologies such as the thickness of a knot and the rope length of a knot. They then review the main results in this field. The topics include results on the global minimum rope length of knots, various lower and upper rope length bounds of knots in terms of their crossing numbers, and lower and upper bounds on the total curvatures of thick knots. Some special families of knots or under different settings, such as lattice knots and smooth knots are also considered. While some proofs are omitted or only outlined due to the page limitation of the book, many important ideas, methods, and theorems are explained in depth. At the end of the book, a list of some open problems in this field is given.