Supersymmetry is a symmetry between a boson and a fermion. Although there is no apparent supersymmetry in nature, its mathematical consistency and appealing property have led many people to believe that supersymmetry may exist in nature in the form of a spontaneously broken symmetry. In this talk, I will explore an alternative possibility by which supersymmetry is realized in nature, that is, supersymmetry dynamically emerges in the low energy limit of a non-supersymmetric condensed matter system. I will discuss a (non-supersymmetric) 2+1D lattice model of bosons and fermions whose quantum critical point between a normal phase and a Bose condensed phase shows an emergent space-time supersymmetry. The critical point is described by the Wess-Zumino theory with four supercharges.