Bronchiectasis is defined as the permanent and abnormal dilatation of bronchi. Although it is primarily a pathological diagnosis, CT scanning serves as an excellent surrogate for its detection. This chapter discusses the different types of bronchiectasis and systematically explores the various conditions that could result in the condition. The discussion encompasses the pathogenesis and special imaging features of the various potential etiologies. A section on the diagnostic approach to cystic-fibrosis bronchiectasis also appears in this chapter.