Non-accreting neutron stars display diverse characteristics, leading us to
classify them into several groups. This chapter is an observational driven
review in which we survey the properties of the different classes of isolated
neutron stars: from the 'normal' rotation-powered pulsars, to magnetars, the
most magnetic neutron stars in the Universe we know of; from central compact
objects (sometimes called also anti-magnetars) in supernova remnants, to the
X-ray dim isolated neutron stars. We also highlight a few sources that have
exhibited features straddling those of different sub-groups, blurring the
apparent diversity of the neutron star zoo and pointing to a gran unification.Comment: Invited chapter for Handbook of X-ray and Gamma-ray Astrophysics
(Section Eds. V. Doroshenko, A. Santangelo; Eds. C. Bambi and A. Santangelo,
Springer Singapore, 2023