In the post-genomic era, high-resolution determination of protein and virus
structures becomes extremely important for accurate interpretations
of biological functions at the molecular level. The three-dimension (3D)
reconstruction of macromolecular structures from 2D electron microcopy
images of frozen hydrate samples (CryoEM) has many advantages over other
imaging techniques. In particular, it allows us to capture the structure
of macromolecules in their native states.  However, in order to perform
a successful reconstruction, one has to solve a variety of difficult
computational problems.  The purpose of this talk is to provide
an overview on computational problems encountered in CryoEM reconstruction
and the state-of-art algorithms for solving these problems.