Although Thomas Young is generally given credit for being the first to provide evidence against Newton s corpuscular theory of light, it was Augustin Fresnel who first stated the modem theory of diffraction. We review the history surrounding Fresnel s 1818 paper and the role of the Poisson spot in the associated controversy. We next discuss the boundary-diffraction-wave approach to calculating diffraction effects and show how it can reduce the complexity of calculating diffraction patterns. We briefly discuss a generalization of this approach that reduces the dimensionality of integrals needed to calculate the complete diffraction pattern of any order diffraction effect. We repeat earlier demonstrations of the conventional Poisson spot and discuss an experimental setup for demonstrating an analogous phenomenon that we call a "second-order Poisson spot." Several features of the diffraction pattern can be explained simply by considering the path lengths of singly and doubly bent paths and distinguishing between first- and second-order diffraction effects related to such paths, respectively. (C) 2009 American Association of Physics Teachers. [DOI: 10.1119/1.3119181]