Knot theory is only a century old. Its has lead to applications in DNA research and the synthesis of new molecules, and is having a significant impact on statistical mechanics and quantum field theory. What are the properties and classifications of knots ? How do you determine whether a knot is actually knotted or can be untangled ? This introduction to the fascinating world of knots will provide insight in these questions, exploring problems, established theorems, as well as those that remain open.