  This is a short arrangement of notes on D-branes, offered as an embellishment
of five lectures which were presented at the 1998 Trieste Spring School
entitled ``Non-Perturbative Aspects of String Theory and Supersymmetric Gauge
Theory''. There is a good number of collections of pedagogical notes on
D-branes in the literature, and since space here is limited, no attempt will be
made to cover all of the introductory material again. Instead, the notes cover
selected topics and themes in string theory and M-theory, emphasizing how
certain technical aspects of D-branes play a role. The subject is developed
mainly from the perspective of non-perturbative string theory, touching on
aspects of the old matrix model, string duality, the new matrix model, the
AdS/CFT correspondence and other gauge theory/geometry correspondences.
