Chapter 3

In spite of almost four decades of intensive research on pulsars, it is a fair statement that pulsars are understood only poorly. The `pulsar problem' is considered as one of the most difficult ones in modern astrophysics (see, for example, Bahcall and Ostriker (1997)) as it consists in fact of a range of unsolved problems. The questions to be answered address: (a) pulsars as neutron stars (e.g. What is the structure of neutron stars? or What is the composition of neutron star atmospheres?); (b) the surroundings of pulsars (e.g. What is the structure of the magnetic and electric fields?, What are the plasma densities? or Are there regions of additional pair creation and how does that work?); (c) the radiation processes themselves (e.g. What is the radio emission mechanism? or How and where is the high-energy emission created?).