The LAMOST experiment for Galactic Understanding and Exploration (LEGUE) plan to study the structure of the Galactic halo both the smooth component of the spheroid and the lumpy sub-structure) and disk components (including star-forming regions and open clusters (OCs)).With the data representing a huge number of stars from the LAMOST spectroscopic survey, stellar kinematics can be calculated and the metallicity distribution function (MDF) in the Galaxy will be obtained. This will allow us to systematically investigate the spatial density, Galactocentric rotation velocity and velocity ellipsoid, and chemical abundance of stars as a function of position in the Galaxy.

These provide important constraints on the present models for Galactic structure, formation history, kinematical and dynamical evolution, chemical evolution, and the distribution of dark matter in the Milky Way.
The primary science drivers of the LAMOST Galactic structure survey are:

1)Search for extremely metal poor stars in the Galactic spheroid;

2)Kinematical features and chemical abundances of the thin/thick disk stars, with the goal of deriving the mass distribution (including the dark matter mass), the dynamical and chemical evolution, and the structure and the origin of the Galactic disks;

3)A through analysis of the disk/spheroid interface near the Galactic anticenter, with the goal of determining whether previously identified anticenter structures are tidal debris, or whether they are part of structure in the disk;

4)Discovery of stellar moving groups that may be associated with dwarf galaxies, and follow-up observations of known streams and substructures in the Galactic spheroid;

5)Survey of the properties of Galactic OCs, including the structure, dynamics and evolution of the disk as probed by OCs;

6)Search for hypervelocity stars and determination of their creation mechanism;

7)Survey the OB stars in the Galaxy, tracing the 3D extinction in the Galactic plane;

8)A complete census of young stellar object across the Galactic Plane, which provide important clues to studies of large-scale star formation and the history of Galactic star formation.