Critical phenomena are inherent to those critical systems whose macroscopic properties depend on few physical parameters and in addition, these properties have a universal character. Among these, we can quote materials that exhibit a critical point, long-polymers in solution, particles aggregates, percolating systems, sol-gel transition and so on. Under special conditions, the bilayer biomembranes can also undergo phase transitions. Typical examples are lateral and transversal phase separations and unbinding phase transition (membrane adhesion). In this study, we review on new findings dealt with these phase transitions.