  Structure functions of the spin-1 deuteron will be investigated
experimentally from the late 2020's at various facilities such as Thomas
Jefferson National Accelerator Facility, Fermi National Accelerator Laboratory,
nuclotron-based ion collider facility, and electron-ion colliders. We expect
that a new high-energy spin-physics field could be created by these projects.
In this paper, the current theoretical status is explained for the structure
functions of spin-1 hadrons, especially on parton distribution functions,
transverse-momentum dependent parton distributions, and fragmentation
functions. Related multiparton distribution functions are also shown.
