During the period 1934–1963, electron microscopy emerged from a pioneering imaging technique into a systematic scientific instrument. The dominant themes include the development of theoretical and practical understandings of resolution, contrast, and image formation, driven by improvements in focusing, illumination, aperture control, and aberration management. Researchers emphasized establishing robust sample preparation workflows, such as fixation, staining, and embedding, that enabled reliable ultrastructural visualization across diverse biological and materials applications. The collaborative evolution of optics and preparation methods fostered a cohesive framework guiding subsequent refinements and standardization in electron microscopy.