This lecture explores the concept of isospin symmetry in particle physics, focusing on the symmetry properties of quarks and baryons. It delves into the application of isospin to derive hadron wave-functions and introduces the SU(2) symmetry group. The lecture also discusses the conservation laws associated with isospin and the formation of baryon wave-functions. Additionally, it covers the combination of quarks, the properties of isospin, and the decay patterns of Delta resonances.