After a short description of the historical discovery of pulsars, the different possible interpretations for pulsars are discussed. The different observational classes of pulsars are summarized. The dipole model for pulsars is introduced to motivate the definition of the characteristic age and the magnetic field of pulsars. The notion of the braking index of pulsars is confronted with the dipole model and the emission of gravitational waves from pulsars. The pulsar diagram is discussed in terms of the evolution of pulsars and the recycling mechanism for binary pulsars. The model of the aligned rotator introduces the magnetosphere of pulsars and a more sophisticated approach for the pulsar emission mechanism. The details of extracting the neutron star masses from pulsar timing is outlined. Observational data from the Hulse–Taylor pulsar and the double pulsar are confronted with predictions from general relativity in strong fields.