  This is the first paper of a series devoted to studying the population of
blue massive stars in NGC 55, a galaxy of the Sculptor group at a distance of
about 2 Mpc. We have obtained optical (3300-6210A) low-resolution spectra of
blue massive stars with VLT-FORS2, which we have classified with the aid of
Milky Way and Magellanic Cloud standard stars.
  We have developed the first census of massive blue stars in NGC 55. A study
of stellar radial velocities shows agreement with existing HI rotational
velocity curve work and reveals the presence of one object with peculiar
velocity. A qualitative study of the stellar metallicity suggests that its
global distribution over NGC 55 is close to that of the LMC, as derived from
previous studies. We present a catalogue with 164 classifications of blue
massive stars in NGC 55. This catalogue is a first and necessary step for the
subsequent quantitative study of blue massive stars in NGC 55 with
state-of-the-art models.
