  Uncertainties in stellar structure and evolution theory are largest for stars
undergoing core convection on the main sequence. A powerful way to calibrate
the free parameters used in the theory of stellar interiors is
asteroseismology, which provides direct measurements of angular momentum and
element transport. We report the detection and classification of new variable O
and B stars using high-precision short-cadence (2-min) photometric observations
assembled by the Transiting Exoplanet Survey Satellite (TESS). In our sample of
154 O and B stars, we detect a high percentage (90%) of variability. Among
these we find 23 multiperiodic pulsators, 6 eclipsing binaries, 21 rotational
variables, and 25 stars with stochastic low-frequency variability. Several
additional variables overlap between these categories. Our study of O and B
stars not only demonstrates the high data quality achieved by TESS for optimal
studies of the variability of the most massive stars in the Universe, but also
represents the first step towards the selection and composition of a large
sample of O and B pulsators with high potential for joint asteroseismic and
spectroscopic modeling of their interior structure with unprecedented
precision.
