Although the existence of Oort’s cometary cloud has been generally accepted, his hypothesis on its origin has been repeatedly called into question, in particular because of the large mass that Jupiter would also have simultaneously ejected out of the solar system. However, the extremely slow growth of particles in regions of small density seems to rule out that comets condensed “in situ” at their present large distances. Also, the accumulation of interstellar grains in satellite disks orbiting around the primitive solar nebula seems an “ad hoc” hypothesis that cannot be proved or disproved. Therefore, the most reasonable hypothesis is that comets were ejected from the region of the giant planets as a natural by-product of their accretion.