Proteins carry out a variety of vital functions in every living organism, ranging from enzyme proteins regulating biochemical reactions to motor proteins causing the contraction and movement of muscles. The three-dimensional shape of proteins is crucial for their biological function. This book investigates the protein folding problem from two different angles. The first is the question how a protein's amino acid sequence determines its structure, the second aspect is the physical process of protin folding. Both questions are addressed using so-called structural profiles as one-dimensional representations of protein structure.