Every physics and optical engineering student learns that an arbitrary optical wave field can be decomposed into a superposition of (Huygens’) spherical wavelets, i.e., the Rayleigh–Sommerfeld diffraction theory. They also learn that an arbitrary optical wave field can be decomposed into a superposition of plane wave components, i.e., the angular spectrum approach of Fourier optics. Meanwhile, the alternative method of decomposing an arbitrary optical wave field into a superposition of Gaussian beamlets (this terminology, in analogy to the well-known Huygens’ spherical wavelets, was introduced by Al Greynolds in ^{2}) has been implemented by software engineers in several commercially available software packages. These software packages are being extensively used by industry and government agencies to model the physical optics performance of increasingly advanced optical systems, including the polarization and coherence characteristics of those systems. The resulting software is fast, accurate, user-friendly, provides impressive graphical output, and can potentially be used as a great tool in education for illustrating a wide variety of physical optics phenomena.