Today, the proton is seen as a dynamic system with three valence quarks and a sea of quarks and antiquarks that radiate gluons and gluons that split into quark-antiquark pairs or into two gluons. These processes are described by the theory of the strong force --- the Quantum Chromodynamics (QCD). This book presents a study of the structure of proton as probed at HERA (Hadron Electron Ring Accelerator) using a set of parton distribution functions (PDFs) based on self-similarity. This new approach to study the proton structure by looking at the fractal patterns in the parton densities at small...