A common class of astrophysical systems consists of smaller bodies or biting a more massive central object. The orbits of the smaller bodies usually change over their lifetime, this is referred to as orbital migration. Resonance—where two system frequencies align—is one of the strongest indicators of smooth orbital migration, as the sweeping of frequencies over time enables capture. For example, many exoplanet systems have been observed to be in mean motion resonance, where their orbital periods are related by an integer ratio. This configuration is usually attributed to smooth, disk-driven migration. In this thesis, I investigate three topics concerning migration and resonance. The first topic I investigate is the effect of gas accretion on a migrating planet. I show that orbital migration is outward in my model, contrary to the classic picture of planet migration. Secondly, I determine the disk conditions which lead to apsidal alignment and anti-alignment in resonant exoplanet systems. I demonstrate that a force which drives eccentricities can potentially explain aligned systems. Lastly, I study the effect that differential apsidal precession has on resonance capture. I identify both a resonance overlap threshold and a secular resonance that can disrupt capture.