ABSTRACT: Stellar occultations are a powerful tool to study bodies located at billions of km from
Earth. Accuracy on size determination can be sub-kilometric. Also, tenuous atmospheres like those 
of Pluto and Triton can be detected through this method. Recent results include the discovery of a 
spectacular two-fold increase of Pluto's atmospheric pressure between 1988 and 2002, and 
stabilization after that date, kilometric accuracy for the sizes of Charon and Titania, and upper 
limits of 15 to 110 nanobar for the surface pressures of putative atmospheres for those latter 
bodies.  The next step is now to detect stellar occultations by the largest (~1000km or more) and 
the smallest (~1 km or less) Trans-Neptunian Objects (TNO's). Potential scientific returns are (1) 
measure of TNO sizes and shape at sub-km accuracy, (2) calculation of densities for those TNO's 
with satellites, whose mass can thus be derived, (3) detection of atmosphere as tenuous as 10 
nanobar for TNO's comparable to Pluto in size, (4) derive size and spatial distribution of the 
smaller TNO's. Ongoing programs on large telescopes (e.g. ToO runs with ISAAC and SOFI, 
Ultraphot/GIRAFFE project) and small instruments (e.g. amateurs) may both contribute to learn more 
about TNO's population. Technical aspects and basic requirements for those experiments will be 
presented.