1. Introduction. A popular - often textbook supported- view is that the diffraction limit of large telescopes is out of reach from ground-based observatories.

We summarize on Fig.1 the scope of angular resolving power, in the range lOOnm to 10. nm, as it appears today.

A quick look reveals, expressed in absolute angular terms, a number of stimulating points :

(i) recent advances in speckle techniques allow to reach the diffraction limit of large ground-based telescopes, notwithstanding the seeing effects. Initially devised to measure double bright stars separation in the visible, these techniques have been extended to weak visible stars (mv ~ 14 to 16), to infrared sources (l-5µm), to full image reconstruction, and even to diffraction limited images obtained with optics suffering from residual aberrations (Faint Object Camera on the Space Telescope);