I briefly review information on the effects and incidence of minor mergers as they affect the growth of galaxy disks. Useful constraints can come from statistics of galaxy interactions and stellar demographics in the halos of nearby galaxies (including our own). The low luminosity of the typical galaxies at issue means that empirical data on the evolution of minor mergers are sparser than for the major mergers most relevant to production of elliptical remnants, so that indirect measurements such as the epoch of appearance of dynamically organized disks in luminous galaxies become important. I conclude by discussing the interplay of star formation and the hot ISM in the survival of dust in the disks, which may be important in the shutdown of star formation in quiescent S0 disks whether their star formation results from secular processes or recently-acquired gas.

At luminosities above 10¹¹ L(Sun), the space density of far-infrared selected galaxies exceeds that of optically selected galaxies. The Luminous Infrared Galaxies (LIRGs) are primarily interacting or merging disk galaxies undergoing enhanced star formation and Active Galactic Nuclei (AGN) activity, possibly triggered as the objects transform into massive S0 and elliptical merger remnants. We have obtained ACS/WFC imaging of 88 LIRGs with L_IR>10^11.4 L(Sun) from the IRAS Revised Bright Galaxy Sample (60 micron flux density > 5.24 Jy). This sample is ideal not only in its completeness and sample size, but also in the proximity and brightness of the galaxies. The superb sensitivity, resolution, and field of view of ACS on the Hubble Space Telescope enables a unique opportunity to study the detailed structure of galaxies that sample all various stages of the merger process. Imaging has been done with the F435W and F814W filters (B and I-band) to examine as a function of both luminosity and merger state the structural properties (AGN, bulge, and disk components) and fundamental parameters (effective radius and surface brightness) of LIRGs and their similarity with putative evolutionary byproducts (elliptical and classical AGN host galaxies). Morphological analysis shows a mixture of early and late-type galaxies at all stages of the interaction. The morphology and concentrations of post-interactions will be presented.

The merger histories of galaxies are interesting both for studying the stability of galactic disks and the transformation of disk galaxies into spheroids. I will review what is known about galaxy mergers in hydrodynamical simulations. In our simulations we find that major mergers are quite rare and that most galaxies have not had one since z~2. The merger rate is a strong function of galaxy mass, which can explain the observed trend of Hubble type with stellar mass. In addition I will discuss new work calculating merger rates in N-body simulations where we find that for dark matter halos 1:10 mergers are very common. How the Milky Way's disk manages to survive such mergers is thus an interesting question.

Interactions between late type galaxies dramatically change their morphology and by redistributing their gas, enhance the star formation rate in them. I will review the mid infrared properties of interacting galaxies as these were revealed using observations from the Infrared Space Observatory and Spitzer Space Telescope over the last decade. The variation of their observed spectral energy distributions in the infrared is used as tracer of the physical mechanism dominating the energy production in these systems and their connection to the properties of ultra-luminous infrared galaxies will be presented.

The incidence, location, and origin of young stars and star formation in nearby early-type galaxies are constrained from multi-wavelength observations. Relying primarily on two-dimensional maps of the ionized-gas and stellar absorption linestrengths from SAURON, I will briefly discuss the distributions of age and metallicity in local early-types and review the evidence for recent star formation. Particular attention will be paid to the apparent relationship between young stars and kinematically decoupled components such as central disks, suggesting recent accretion or merging events. Complementary evidence for both internal and external star formation drivers will also be presented from our parallel GALEX UV imaging survey. I will further discuss at length a new survey of the molecular gas in SAURON galaxies, as well as ongoing targeted mm synthesis observations of a number of galaxies in CO, on the same spatial scales as the integral-field data. Those indicate a surprisingly high star formation efficiency in early-types and show stunning correlations between molecular gas structures and young dynamically decoupled components. In particular, a number of objects in the process of forming regular kpc-size disks are revealed. Taken together, our observations offer a fairly complete picture of residual star formation in early-types and reveal disk formation in real time, in a setting probably not unlike that of disk formation in dark halos at high redshifts.