The normal development and microanatomy of the pancreas are summarized, and brief comments are made regarding current concepts of the control of exocrine functions. Pathologic alterations of acinar cells (including degranulation, nuclear changes, and cytoplasmic vacuolization) are fairly common, but they are often overlooked. Dilatation of acini, loss of acinar cells, and apparent increases in centroacinar cells and intercalated ductal cells also may occur. Changes in the larger ducts include epithelial atrophy, hyperplasia, and metaplasia; in addition, some relationships to age, ductal obstruction, and ductal carcinoma may exist. However, the majority of the alterations are nonspecific. The major types of chronic pancreatitis are illustrated, especially the irregularity of the pancreatic involvement that is so common. In an attempt to better understand the early stages of acute pancreatitis, foci of acute localized pancreatitis have also been studied.