Min-Kai Lin, an astrophysicist with ASIAA visiting the Institute for Advanced Study, presents a seminar on how gas and dust interact in protoplanetary disks to build planets. He covers hydrodynamic instabilities in the cold, planet-forming regions of disks, including the vertical shear instability and convective overstability, and explains how these can both hinder dust growth through turbulence and help it by creating large structures that concentrate dust. The talk extends the classical streaming instability, used to explain planetesimal formation, to account for more realistic conditions such as accretion flows and magnetic fields. Lin discusses open problems these refinements raise and proposes new pathways for planetesimal formation that might account for how common planets appear to be across the universe. The seminar is aimed at researchers in astrophysics and planetary science, drawing on recent analytical and numerical studies.