  An {\em ab initio} (i.e., from first principles) theoretical framework
capable of providing a unified description of the structure and low-energy
reaction properties of light nuclei is desirable to further our understanding
of the fundamental interactions among nucleons, and provide accurate
predictions of crucial reaction rates for nuclear astrophysics, fusion-energy
research, and other applications. In this contribution we review {\em ab
initio} calculations for nucleon and deuterium scattering on light nuclei
starting from chiral two- and three-body Hamiltonians, obtained within the
framework of the {\em ab initio} no-core shell model with continuum. This is a
unified approach to nuclear bound and scattering states, in which
square-integrable energy eigenstates of the $A$-nucleon system are coupled to
$(A-a)+a$ target-plus-projectile wave functions in the spirit of the resonating
group method to obtain an efficient description of the many-body nuclear
dynamics both at short and medium distances and at long ranges.
