Millisecond pulsars represent an evolutionarily distinct group among rotation-powered pulsars .
Outside the radio band , the soft X-ray range ( \sim 0.1 –10 keV ) is most suitable for studying radiative mechanisms operating in these fascinating objects .
X-ray observations revealed diverse properties of emission from millisecond pulsars .
For the most of them , the bulk of radiation is of a thermal origin , emitted from small spots ( polar caps ) on the neutron star surface heated by relativistic particles produced in pulsar acceleration zones .
On the other hand , a few other very fast rotating pulsars exhibit almost pure nonthermal emission generated , most probably , in pulsar magnetospheres .
There are also examples of nonthermal emission detected from X-ray nebulae powered by millisecond pulsars , as well as from pulsar winds shocked in binary systems with millisecond pulsars as companions .
These and other most important results obtained from X-ray observations of millisecond pulsars are reviewed in this paper , as well as results from the search for millisecond pulsations in X-ray flux of the radio-quite neutron star RX J1856.5–3754 .

\PACS 95.85.Nv 97.10.Qh 97.60.Jd 97.60.Gb