  Since the 1990's, protoplanetary disks and planetary disks have been
intensively observed from the optical to the millimetre wavelength and many
models have been developed to investigate their gas and dust properties and
dynamics. These studies remain empirical and rely on poor statistics with only
a few well known objects. However, the late phases of the stellar formation are
among the most critical for the formation of planetary systems. Therefore, we
believe it is timely to tentatively summarize the observed properties of
circumstellar disks around young stars from the protoplanetary to the planetary
phases. Our main concern is to present the physical properties considered as
observationally robust and to show their main physical differences associated
to an evolutionary scheme. We also describe areas still poorly understood such
as how protoplanetary disks disappear to lead to planetary disks and eventually
planets.
