From man's earliest attempts to manufacture tools and cloths and construct buildings, he has faced health risks from inhalable substances or dusts in the workplace. With sophistication of life and creation of villages, cities and societies, such risks became more serious. Fibrosis is the abnormal production of collagen fibers following tissue damage. This accounts for the formation of scar tissue. Lung fibrosis is one of the typical ways in which the lung reacts to damaging stimuli. Historically, idiopathic pulmonary fibrosis was thought to be a deleterious consequence of persistent lung inflammation that followed an unknown insult. It is clear that novel strategies are required in the treatment of pulmonary fibrosis. Specific anticytokine therapies will require evaluation, used either singly or in combination. In this book, we practically investigated the involving phenomena during the process of bleomycin-induced fibrosis in murine lung.