  In this set of lectures various properties of D-branes are discussed. After
reviewing the basics, we discuss unstable D-brane/anti-D-brane systems, a
subject pioneered by Sen. Following him, we discuss the construction of the
non-BPS D0-brane in type I theory. This state is stable since it carries a
conserved Z_2 charge. The general classification of D-brane charges using
K-theory is discussed. The results for the type I theory, and the T-dual type
I' theory, are emphasized. Compactification of type I on a circle or torus
gives a theory with 16 supersymmetries in 9d or 8d. In each case the moduli
space has three branches. The spectrum of non-BPS D-branes are different for
each of these branches. We conclude by pointing out some problems with the type
I D7-brane and D8-brane predicted by K-theory.
