  Three dimensional topological insulator represents a class of novel quantum
phases hosting robust gapless boundary excitations, which is protected by
global symmetries such as time reversal, charge conservation and spin
rotational symmetry. In this work we systematically study another class of
topological phases of weakly interacting electrons protected by spatial
inversion symmetry, which generally don't support stable gapless boundary
states. We classify these inversion-symmetric topological insulators and
superconductors in the framework of K-theory, and construct their lattice
models. We also discuss quantized response functions of these
inversion-protected topological phases, which serve as their experimental
signatures.
