  This exposition provides a detailed picture of ongoing and planned activities
towards the development of a detector for a high-energy Linear Collider. Cases
for which research and development activity does not exist, or needs to be
bolstered, are identified for the various subsystems. The case is made that the
full exploitation of the potential of a high-energy Linear Collider will
require the augmentation of existing detector technology and simulation
capability, and that this program should become a major focus of the worldwide
particle physics community should the construction of a Linear Collider become
likely.
