The objective of this chapter is to introduce the ventilation homogeneity and lung elasticity. The term lung ventilation refers to the process in which a gas mixture continuously cycles between entering and leaving the air spaces of the lung. Traditional subdivisions of the overall lung ventilation are alveolar space ventilation and dead space ventilation, which refer to the ventilation of air spaces delimited and nondelimited by alveoli, respectively. Molecular diffusion is the principal mechanism of gas mixing in the lung. It is due to the random movement of gas molecules and results in a net transfer of given gas species from regions of high concentration to regions of low concentration. This chapter covers the statics of lung elasticity, dynamics of lung elasticity and physiological methods to study the distribution of ventilation.