  Cosmological observations offer unique and robust avenues for probing the
fundamental nature of dark matter particles-they broadly test a range of
compelling theoretical scenarios, often surpassing or complementing the reach
of terrestrial and other experiments. We discuss observational and theoretical
advancements that will play a pivotal role in realizing a strong program of
cosmological searches for the identity of dark matter in the coming decade.
Specifically, we focus on measurements of the cosmic-microwave-background
anisotropy and spectral distortions, and tracers of structure (such as the
Lyman-$\alpha$ forest, galaxies, and the cosmological 21-cm signal).
