This book is to show the beautiful interior of the atom. The book starts with Democritus, proceeds chronologically through plum pudding model, ‘soft’ atom model, planetary model, ’hard’ atom model. Heisenberg and Schrödinger atom models, Dirac atom model and ends with Hofstadter and Gell Mann. The meaning of Planck constant, similarity between matrix mechanics and wave mechanics, symmetry of the orbital and the reason for the stability of the octet configuration are given. The experiment conducted by David Pritchard from the Massachysetts Institute of Technology to isolate an atom and the Experiment of Stephen Chn to trap atom are given. The experiment conducted by Daniel Walls at the University of Auckland (1991) to demolish the argument of Einstein, Podolsky and Rosen is given. The quarks, leptons and the structure of the nucleon are vividly discussed. The limitation of the standard model is also discussed