Dark matter is one of the most persistent mysteries in modern physics. It is central to particle physics, cosmology, and astrophysics, yet the effort to identify and detect it has grown into an intrinsically interdisciplinary enterprise that involves atomic and nuclear physics, condensed matter physics, chemistry, and precision measurement. Although its gravitational imprint is firmly established, the microscopic nature of dark matter remains unknown. Remarkably, even its characteristic mass scale is largely unconstrained, spanning an enormous range from ultralight wave-like candidates around 10^{-22}\,\mathrm{eV} to macroscopic compact objects up to \sim 10^{35}\,\mathrm{g}. This breadth has motivated a diverse set of theoretical proposals and search strategies across many energy, length, and time scales.

In this colloquium, I will first give a structured overview of the dark matter problem, emphasizing how different mass regimes map onto distinct physical pictures and experimental approaches. I will then focus on a particularly well motivated framework, thermal dark matter, often discussed in connection with WIMPs. Thermal dark matter is defined by the assumption that the dark sector was once in thermal equilibrium with the Standard Model in the early Universe, and that the present day relic abundance was set dynamically through freeze out or closely related mechanisms. This paradigm is compelling because it ties the dark matter density to microphysics rather than initial conditions, is embedded in the successful thermal history of standard cosmology, and connects early Universe interactions to concrete experimental signatures today. Thermal candidates also arise naturally in broad classes of beyond the Standard Model theories, including supersymmetry, grand unification, and hidden sector constructions.

Finally, I will summarize the current landscape of theoretical developments and the status of searches, from collider and intensity frontier probes to direct detection, indirect searches, and cosmological and astrophysical constraints. The goal is to provide a systematic and intuitive picture of where the leading opportunities and challenges lie across mass scales, and what near and mid term prospects may be most promising.