  We present a spectroscopic survey of the stellar population of the Sigma
Orionis cluster. We have obtained spectral types for 340 stars. Spectroscopic
data for spectral typing come from several spectrographs with similar
spectroscopic coverage and resolution. More than a half of stars of our sample
are members confirmed by the presence of lithium in absorption, strong
H$\alpha$ in emission or weak gravity-sensitive features. In addition, we have
obtained high resolution (R~34000) spectra in the H$\alpha$ region for 169
stars in the region. Radial velocities were calculated from this data set. The
radial velocity distribution for members of the cluster is in agreement with
previous work. Analysis of the profile of the H$\alpha$ line and infrared
observations reveals two binary systems or fast rotators that mimic the
H$\alpha$ width expected in stars with accretion disks. On the other hand there
are stars with optically thick disks and narrow H$\alpha$ profile not expected
in stars with accretion disks. This contribution constitutes the largest
homogeneous spectroscopic data set of the Sigma Orionis cluster to date.
