Proteins and nucleic acids are responsible for biochemical pathways and diseases. The function of a protein is related to its three dimensional structure, which confirms evolutionary changes in related species through mutation. As mutations lead to disorders at the molecular level, clear understanding of the nature of a disease depends on precise structure determination of the related proteins. X-ray crystallography is the only field that has won the maximum number of Nobel Prize. This module will highlight, in depth, the scientific, biological and pharmaceutical significance of selected crystal structures and answers the question 'why these structures won the Nobel Prize'.