Knot theory is currently one of the most active research fields in topology. the classical sense it is the study of circles (closed 1-manifold) in Euclidean 3-space or a 3-sphere S3. This is generalized to higher dimensional knot theory and furthermore to the study of manifold pairs or topological space pairs up to homeomorphism (in the topological, PL, or smooth category). Since topology is the study of topological spaces up to homeomorphism, knot theory in this global sense is a quite wide area of topology. Two-dimensional knot theory or knot theory dimension four deals with surfaces in 4-space. We will refer to them as "surface links" in this book.