Planetary astrophysics is the most exciting and fastest growing branch of astronomy today. New data obtained from systematic radial velocity surveys and Kepler transit surveys have led to the discovery of over 700 planets and 3000 additional candidates, many of which are multiple systems. Although their presence is ubiquitous around nearby stars, their kinematic and structure properties appear to be diverse. Based on these rich data, I will present some theoretical analyses which may enable us to extract information about their origin, evolution, and structure. I will discuss the process of planet migration in evolving protostellar disks, the interaction of stellar magnetic fields with protostellar disks and close-in planets, tidal evolution of close-in companions, the potential retention of volatile elements and loss of atmosphere. These effects are incorporated into population synthesis models and the construction of scenarios for the retention of close-in planets and the observed obliquity between stellar spins and planet's orbits.