  String duality suggests a fascinating juxtoposition of world-volume and
target-space dynamics. This is particularly apparent in the $D$-brane
description of stringy solitons that forms a major focus of this article (which
is {\it not} intended to be a comprehensive review of this extensive subject).
The article is divided into four sections:
  1. The oligarchy of string world-sheets
  2. $p$-branes and world-volumes
  3. World-sheets for world-volumes
  4. Boundary states, $D$-branes and space-time supersymmetry
  [This article is based on a talk presented at the CERN Workshop on String
Duality (December, 1995) and the published version of a talk at the Buckow
Symposium (September, 1995).]
