  The Spin Physics Detector (SPD) is a future multipurpose experiment foreseen
to run at the NICA collider, which is currently under construction at the Joint
Institute for Nuclear Research (JINR, Dubna, Russia). The physics program of
the experiment is based on collisions of longitudinally and transversely
polarized protons and deuterons at $\sqrt{s}$ up to 27 GeV and luminosity up to
10$^{32}$ cm$^{-2}$ s$^{-1}$. The SPD will operate as a universal facility for
comprehensive study of unpolarized and polarized gluon content of the nucleon,
using different complementary probes such as: charmonia, open charm, and prompt
photon production processes. The aim of this work is to make a thorough review
of the physics objectives that can potentially be addressed at the SPD,
underlining related theoretical aspects and discussing relevant experimental
results when available. Among different pertinent phenomena particular
attention is drawn to the study of the gluon helicity, gluon Sivers and
Boer-Mulders functions in the nucleon, as well as the gluon transversity
distribution in the deuteron, via the measurement of specific single and double
spin asymmetries.
