A review of the selected results concerning the role of hydrostatic pressure in studies of impurity and defect centers in IIIยฑV nitrides, and in InGaAsN with small amount of N is presented. Firstly, the shallow to deep impurity state transition for basic donors, i.e. Si and O in GaN and AlGaN and their DX-like center behavior is discussed. It corresponds to the localized state of the appropriate donor (resonant with the conduction band at low pressures) which enters the band gap of GaN or Al x Ga 1ยฑ ยฑx N at sufficiently high pressure and/or x value. Next, the concept of pressure application to prove the effective mass character of Mg acceptor in GaN is demonstrated. We also present results of an anomalous decrease of the pressure coefficient with increasing amount of In in In y Ga 1ยฑ ยฑy N for photoluminescence and electroluminescence. It is compared with the pressure induced changes of the photocurrent spectrum in green Nichia diodes which we consider as corresponding to the variation of the In y Ga 1ยฑ ยฑy N band gap with pressure. Finally, studies of the peculiarities of the conduction band structure and related transport properties as a function of pressure in InGaAsN are presented.