Abstract. Although the standard paradigm of Cold Dark Matter (CDM) has been remarkably successful in predicting the large-scale structure of the universe, it has been known to exhibit a number of problems at small scales. A popular solution to these problems involves invoking Warm Dark Matter (WDM) particles of mass about keV that erase small-scale power. The mass of these WDM particles can, in principle, be constrained using cosmological observations at high redshift. In this talk, we will explore various observational probes and the corresponding theoretical formalism which can be useful for constraining the nature of dark matter using ongoing and upcoming instruments.