The lung is affected by a variety of disease processes that can lead to considerable morbidity and mortality. As the lung is the only organ for respiration and gas exchange, the structural and functional integrity of the lung is of primary importance. Various pathological processes affect the extracellular matrix (ECM) of the lung in an adverse manner, causing destruction of tissue integrity followed by tissue remodeling, which together impair normal pulmonary function. Matrix metalloproteinases (MMPs) are neutral proteinases that are involved in the breakdown and remodeling of the ECM under a variety of physiological and pathological conditions. MMP-2 and MMP-9, collectively known as the gelatinases, are particularly important in the pathogenesis of inflammatory, infectious, and neoplastic diseases in many organs including the lung. This review examines the expression of MMP-2 and MMP-9 in disease of the lung and discusses the role these gelatinases may play in disease progression.