  In a first part, I review our detailed investigation of the prospects to
discover deep-inelastic processes induced by small QCD-instantons at HERA. This
includes the essence of our calculations based on instanton-perturbation
theory, crucial lattice constraints and a confrontation of the recent
intriguing (preliminary) search results by the H1 collaboration with our
predictions. In a second part, I report on two ongoing attempts towards a
better understanding of the role of larger-size instantons in the QCD-vacuum
and in high-energy (diffractive) scattering processes, respectively: The
striking suppression of larger-size instantons in the vacuum is attributed to a
residual conformal inversion symmetry, and a precocious lack of ``color
transparency'' in the one-instanton contribution to the color-dipole scattering
picture is emphasized.

High Energy Physics - Phenomenology