Planets are built from planetesimals, themselves built from small dust grains in gaseous protoplanetary discs. Understanding how small grains interact with the gas flow is fundamental to any planet formation theory. However, coupling gas dynamics with solids is a challenging problem for both analytical and numerical calculations. I present a novel framework to study dusty-gas interaction in protoplanetary discs. I describe how this problem is analogous to pure gas dynamics with heating and cooling. It is thus possible to understand dusty-gas dynamics in the language of standard, textbook hydrodynamics. I will demonstrate several applications of this framework, including the streaming instability for planetesimal formation, dust-trapping by pressure bumps, dust-settling, and dusty disc-planet interaction. I will also discuss how this framework can be exploited to find new phenomena in dusty protoplanetary discs.