Pulmonary surfactant, a mixture of ~90 wt % lipids and ~10 wt % proteins secreted by the type II epithelial cells, is essential for the normal functioning of the lungs during the respiration cycle. It helps lower the surface tension by forming a surface active film at the air/liquid interface thus reducing the effort required for breathing. It also prevents alveolar collapse after expiration. Low amounts of pulmonary surfactant in the alveolar space of neonates results in Respiratory Distress Syndrome (RDS). Deactivation of pulmonary surfactant is also known to exacerbate Acute Respiratory Distress Syndrome (ARDS). Endogenous pulmonary surfactant is a complex mixture of phospholipids and proteins. Dipalmitoylphosphatidylcholine (DPPC), a major component of the mixture (~40 wt %), can form a tightly packed gel phase at physiological temperatures and reduce the surface tension to near-zero values. The commonly held view with respect to surfactant function is that the surface film is able to withstand high surface pressures after expiration through the enrichment of the film with DPPC. Two possible mechanisms have been proposed for DPPC enrichment viz. selective DPPC adsorption from the underlying subphase that acts as a lipid reservoir to the monolayer and the selective removal or “squeezing out” of other lipid components from the monolayer to the subphase during compression. Both mechanisms are thought to occur. The surfactant protein SP-B is thought to play a major role in the surface film refinement. The common recourse in cases of RDS is to use surfactant replacement therapy (SRT) in which exogenous surfactant is introduced to reduce the effort required for breathing. The first generation of SRT mixtures in use included DPPC along with chemical spreading agents. Although vastly useful relative to existing options, they were of limited efficacy. The second generation involved the addition of SP-B derived from the lavage of animal lungs. The concerns regarding microbial contamination with such mixtures required elaborate purification methodology leading to the high cost of the product. The third generation currently under clinical testing involves the use of synthetic peptide replacements for SP-B in the SRT regimen thereby lowering the production costs. We present results regarding the surface activity and monolayer structure of such mixtures at the air/water interface obtained from molecular dynamics simulations based on a coarse-grained model of phospholipids and proteins. The current work is part of a multi-scale modeling approach to the study of the dynamics of pulmonary surfactant during the respiration cycle. As a component of this approach, the coarse-grained study will feed into the available knowledgebase of pulmonary surfactant function under physiological conditions and subsequent integration is then proposed with macroscopic simulations of the system.