In 1999, we specialized in 2D seismic depth processing. It was necessary to progress into 3D depth migration, but it seemed unrealistic to utilize Kirchhoff or wave-equation methods and be able to compete with large companies, their compute resources, and their economies of scale. Consequently, it was decided to attempt the commercial development of an alternative approach that would hopefully provide similar or improved technical quality, but with capital outlay and economics that were more appropriate to a small company. A very straightforward approach referred to as beam prestack depth migration (BPSDM) was adopted; its origins dated to work performed in the 1930s by Frank Rieber. The anticipated merits of BPSDM were overall simplicity, economy, flexibility, and future development possibilities. The unknowns were the migration accuracy and quality achievable. BPSDM was essentially developed independently, but aspects of it obviously are related to much recently published work on other beam migrations and stereotomography.