In this final lecture of the series, Feynman discusses the problems which motivated the development of Quantum Electrodynamics, and further problems in the Standard Model of Particle Physics. This includes the Electroweak Theory developed by Steven Weinberg, Abdus Salam and Sheldon Glashow, describing the change of particle flavour by means of a type of neutral current which is asymmetric in nature (found in the study of neutrino flavour change in neutrino detectors and the helicity of neutrinos from the polarisation of beta decay experiments found earlier by Chien-Shiung Wu and her colleagues) and in the detection of particles which break the symmetry in electrodynamic and weak interactions, namely the Z-boson wose S matrix matches that of a photon at energies exceeding 100GeV, giving the so-called Electroweak Force. Moreover, the theory of Nuclear Interactions, in and of themselves, was discovered prior to this, and the interaction of force-carrier particles in the nucleus assumed to exist as a type of propagating Residual Strong Nuclear force which acts in the potential well of the nucleus, gaining strength away from the nuclear well asymptotically. This explains the missing mass of the atoms (pions) and the relativistic properties of these particles within the ranges between the proton and neutron. By detecting high energy cosmic rays and the cascade particles from particle accelerator experiments, a zoo of particles, mesons and baryons was created which were organized in baryon octets and extended into baryon decouplets as new particles were detected with different characteristics (strangeness and charm quantum numbers) which influenced their decay transitions. Such decay transitions required force carriers and certain rules for transition, which did not induce flavour change but a new force called the color force, or the True Strong Nuclear force. For this force to be conceivable, new particles were required called quarks to describe the decay modes. Hence, Quantum Chromodynamics was born from the mind of Murry Gell-Mann. This theory describes gluons in high order interactions, with probabilities in excess of QED. The interactions were very difficult to Feynman, and he preferred to use the parton theory, which is an approximation to QCD and describes very-high energy interactions accurately due to the relative time-dilation of the ultra-relativisitic particles inside baryonic matter that "ignore" intermediates. Feynman, though legendary, did not fully grasp the rule-based QCD interactions which required many intermediates to give numerical results and the polarisation of the particles produced in jets from QCD experiments with heavy ion colliders built in the late 80's and early 90's, which were years after his death.