Principle objective of this lecture is to presentation on Hemoglobin, Portrait of a Protein in Action. This lecture briefly discuss on Hemoglobin and Myoglobin, these are conjugated proteins. A simple protein has merely a polypeptide chain. A conjugated protein has a non-protein part in addition to a polypeptide component. Both myoglobin and hemoglobin contain heme. Here also explain Aromatic Heme, Iron in Hemoglobin binding O2, Iron in Myoglobin binding O2, Resonance in Iron binding O2, Allosteric Proteins and Binding of bisphosphoglycerate.