Luminous Infrared Galaxies (LIGs) are locally more numerous than normal galaxies, AGN, and QSOs above L ˜ 1011
⊙ and may be the evolutionary precursors of classical radio-quiet quasars. VLBI observations of a complete sample show that high-T
radio cores are common, perhaps universal among LIGs. VLBI imaging shows that these radio cores may be produced by intense starbursts which generate luminous radio supernovae, as in the case of Arp 220 (Smith et al. 1998), or by a classical AGN core, as in the case of Mrk 231, which we interpret as a newly formed QSO emerging from a starburst. Compact OH 1667MHz maser emission appears to be common in LIGs and may be related to AGN activity. These results lend further support to the scenario suggested by Sanders et al (1988) in which mergers of gas-rich galaxies lead first to luminous starbursts which evolve into radio-quiet quasars.