We employ and extend the tools of seismology to probe the Earth's deep interior. This involves tackling planetary-scale geophysical problems using new techniques that reconcile and fit concurrently a wide variety of seismological observations. The overarching objective is to create the next-generation three-dimensional images of the Earth’s interior, similar to a CT-scan for the human body. We infer the modeled properties in terms of the dynamics and evolution of the Earth's interior. Along the way, we disseminate research products to the community in the form of data, theory, models and software. Our novel methodologies also lead to a better understanding of devastating earthquakes. The major themes of our research are provided below.