  We use the formulation of the quantum mechanics of first quantized
Klein-Gordon fields given in the first of this series of papers to study
relativistic coherent states. In particular, we offer an explicit construction
of coherent states for both charged and neutral (real) free Klein-Gordon fields
as well as for charged fields interacting with a constant magnetic field. Our
construction is free from the problems associated with charge-superselection
rule that complicated the previous studies. We compute various physical
quantities associated with our coherent states and present a detailed
investigation of their classical (nonquantum) and nonrelativistic limits.
