These course notes document the lecture series from the 1999 Summer School. The lecture material was chosen to emphasize the development of ground-based interferometry and to include an introduction to the future possibilities of space missions within NASA’s Origins Program. The material contained in the course notes is, however, primarily concerned with ground-based interferometry. Plans for space-based interferometry, although not described here, are well represented in the JPL publications describing the Space Interferometry Mission and the Terrestrial Planet Finder (see Appendix B). Although most subjects are covered in detail in their respective chapters, certain subjects, such as the use of fiber optics, spatial filters, and adaptive optics, are mentioned only in passing. Some omissions were inevitable due to the limited scope of the Summer School, and so resources for further reading are included in the Appendices. The course notes are divided into 7 parts and 18 chapters covering the major themes presented during the school. When reading from one chapter to another, please bear in mind that the notation is only consistent within individual chapters.