This talk will introduce the concept of ``pseudo-criticality’’ and discuss its implication for phase transition theories. We will elucidate the pseudo-criticality is instrumental in unraveling the mysteries of complex conformal field theories and illuminating a variety of intriguing physical problems, including weakly first-order transitions in statistical mechanics and the conformal window of gauge theories. Moreover, we will discuss the deconfined criticality in (2+1)d—the quantum phase transition between a Néel antiferromagnet and a valence-bond solid —may actually be pseudocritical, in the sense that it is a weakly first-order transition with a generically long correlation length.