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In the standard model (ΛCDM) galaxies form and evolve within underlying dark matter structures which are assumed to have grown hierarchically. As such there should be observational signatures of the merging process in the structure and dynamics of the remnant galaxy. State-of-the-art high-resolution cosmological simulations have been used to explore three such signatures: the abundance of substructure, the spin and shape of haloes, and the orbital content of these haloes.The Millennium Simulation, combined with semi-analytic galaxy catalogues, is used to compare the predicted frequency of bright central satellites to observations of field and lens galaxies. The predicted frequency is largely independent of galaxy type, but is shown to increase with redshift and halo mass. The predicted frequency is found to be lower than that observed in the Compact Lens All Sky Survey, but considerably higher than that observed in the lens sample of the Sloan Lens ACS Survey and in the field galaxies of the Sloan Digital Sky Survey and the Cosmic Evolution Survey. The distributions of the spin and shape of haloes are explored and the roles of baryons and the physical prescriptions of stellar and black hole feedback are investigated. Baryons act to make the haloes more spherical and are shown to have a significant effect on the shape of the dark matter. The shapes of the simulated haloes are in broad agreement with a wide range of observational estimates of elliptical galaxies. Results of spectral analyses of the orbital content of simulations with different feedback prescriptions are presented. Dark matter only haloes are dominated by box orbits in the central region, but the fraction of box orbits is found to decrease when baryons are included. The orbits of the stellar particles are found to be remarkably similar to those of dark matter particles.

Gravitational microlensing occurs when a massive lens (typically a star) deflects light from a more distant source, creating two unresolvable images that are magnified. The effect is transient due to the motions of the lens and source, and the changing magnification gives rise to a characteristic lightcurve. If the lensing object is a binary star or planetary system, more images are created and the lightcurve becomes more complicated. Detection of these lightcurve features allows the lens companion's presence to be inferred. Orbital motion of the binary lens can be detected in some microlensing events, but the expected fraction of events which show orbital motion has not been known previously. We use simulations of orbiting-lens microlensing events to determine the fraction of binary-lens events that are expected to show orbital motion. We also use the simulations to investigate the factors that affect this detectability. Following the discovery of some rapidly-rotating lenses in the simulations, we investigate the conditions necessary to detect lenses that undergo a complete orbit during a microlensing event. We find that such events are detectable and that they should occur at a low but detectable rate. We also derive approximate expressions to estimate the lens parameters, including the period, from the lightcurve. Measurement of the orbital period can in some cases allow the lens mass to be measured. Finally we develop a comprehensive microlensing simulator, MaBμLS, that uses the output of the Besançon Galaxy model to produce synthetic images of Galactic starfields. Microlensing events are added to the images and photometry of their lightcurves simulated. We apply these simulations to a proposed microlensing survey by the Euclid space mission to estimate its planet detection yield.