  The Atlas3D project is a multi-wavelength survey combined with a theoretical
modeling effort. The observations span from the radio to the millimeter and
optical, and provide multi-colour imaging, two-dimensional kinematics of the
atomic (HI), molecular (CO) and ionized gas (Hbeta, [OIII] and [NI]), together
with the kinematics and population of the stars (Hbeta, Fe5015 and Mgb), for a
carefully selected, volume-limited (1.16*10^5 Mpc^3) sample of 260 early-type
(elliptical E and lenticular S0) galaxies (ETGs). The models include
semi-analytic, N-body binary mergers and cosmological simulations of galaxy
formation. Here we present the science goals for the project and introduce the
galaxy sample and the selection criteria. The sample consists of nearby (D<42
Mpc) morphologically-selected ETGs extracted from a parent sample of 871
galaxies (8% E, 22% S0 and 70% spirals) brighter than M_K<-21.5 mag (stellar
mass M_Star>6*10^9 M_Sun). We analyze possible selection biases and we conclude
that the parent sample is essentially complete and statistically representative
of the nearby galaxy population. We present the size-luminosity relation for
the spirals and ETGs and show that the ETGs in the Atlas3D sample define a
tight red sequence in a colour-magnitude diagram, with few objects in the
transition from the blue cloud. We describe the strategy of the SAURON
integral-field observations and the extraction of the stellar kinematics with
the pPXF method. We give an overview of the characteristics of the other main
datasets already available for our sample and of the ongoing modelling
projects.
