Pulmonary surfactant is a lipid/protein complex crucial to maintain mammalian lungs open, as it facilitates breathing mechanics through a dramatic reduction of surface tension at the air-liquid interface. Intensive research during a few decades has identified many of the molecular actors defining the molecular and biophysical mechanisms of surfactant at the airspaces. Pulmonary surfactant protein SP-B has been undoubtedly identified as the most important and essential molecule to allow for air breathing in the mammalian lungs, as its absence is incompatible with life. We now know that SP-B directs the assembly of surfactant complexes into the lamellar bodies of type II pneumocytes, their secretion, adsorption, and reorganization at the interface as well as the homeostasis of the surfactant layer during different pathophysiological contexts. This review summarizes current models on SP-B structure and biophysical function, supporting how the activity of SP-B may be crucial for the design and production of a new generation of therapeutic products in respiratory medicine.