Several samples have been proposed in the last years in order to study the properties of intrinsically small sources . In this paper , we review the properties of the main samples that are currently available , both selected on the basis of spectral index and of morphology . As a result of the work in this area , large numbers of intrinsically small sources have been found . We summarize the present status of hot spot advance measurements , listing 18 sources with available VLBI data . The mean hot spot separation velocity is v _ { \mathrm { sep } } = ( 0.19 \pm 0.11 ) h ^ { -1 } c and the kinematic ages span the range from 20 to 3000 years . Finally , we present a brief outlook on the use of future instrumentation in order to improve our understanding of radio source evolution . Prospects for VSOP2 , e-VLA , e-MERLIN , LOFAR , ALMA , and Fermi are suggested .