In the following, we shall briefly summarize some facts and ideas concerning the presence of neutron stars in Supernova remnants. While sources similar to the Crab Nebula require the presence of a central energetic object, shell-type remnants such as Cas A are compatible with the presence of neutron stars releasing a weak relativistic wind. Supernova remnants are usually classified into two extreme categories: shelltype and filled-center (plerions). In the case of shell remnants, the edges of the source appear bright, the interior rather faint. The typical radio spectrum is steep (Sν ∝ να with α ' −0.5) and is due to synchrotron radiation from relativistic electrons produced by shocks in the region where the expanding debris interact with the circumstellar/interstellar medium. Cas A is the prototype of shell-type remnants. On the opposite end, the Crab Nebula has been assumed to be the typical plerion, where a central neutron star continuously converts its rotational energy into a magnetized relativistic wind. This wind expands and produces a centerfilled nebular emission which has a rather flat radio spectrum (α ' −0.2). It is not surprising that several remnants show both characteristics (internal emission and bright limbs) since some plerions expand into a relatively dense medium (composite remnants). For more details we refer the reader to a broad review by Frail (1998) and to a full coverage of the subject in the Proceedings of the Arcetri Elba Workshop “Relationship between Neutron Stars and Supernova Remnants” (Bandiera et al. 1998). We also refer to two accompanying papers in these Proceedings which deal with the Crab Nebula (Amato 1999) and with plerions in general (Bandiera 1999). Among the 215 catalogued Supernova remnants (Green 1996) 85% are of the shell-type. In the past, it was widely held that plerions contain a neutron star while shell-type remnants do not, either because the explosion blows apart the entire star or because the central object becomes a black hole. The basis for this belief was the lack of evidence for an internal radio pulsar and/or of a source of relativistic wind. On the other hand, already in the early work on pulsars, it had been suggested that magnetic fields of neutron stars can reach values up to, say, 1014 − 1015 gauss (Woltjer 1968). The initial loss of rotational energy would then be very fast and the central neutron star would soon become unable to produce a strong relativistic wind.