In general, there are two types of animal models: natural and experimental. Because there are no natural models for pulmonary fibrosis, an experimental model that reproduces key aspects of the human disease would be useful for the study of this form of lung disease, the natural history of which is not always known. To date, a variety of animal models have been used to investigate mechanisms of pulmonary and other types of fibrosis, including the intratracheal instillation of bleomycin, fluorescein isothiocyanate, or particulate matter, such as silica and asbestos. This chapter will describe two commonly used techniques, namely bleomycin and silica-induced, which have been developed for the study of pulmonary fibrosis in animal models.