  The three approaches to relativistic generalization of coherent states are
discussed in the simplest case of a spinless particle: the standard, canonical
coherent states, the Lorentzian states and the coherent states introduced by
Kaiser and independently by Twareque Ali, Antoine and Gazeau. All treatments
utilize the Newton-Wigner localization and dynamics described by the Salpeter
equation. The behavior of expectation values of relativistic observables in the
coherent states is analyzed in detail and the Heisenberg uncertainty relations
are investigated.
