The Intermediate Silicon Layers Detector is presently being built as part o
f the CDF upgrades to prepare for the next Tevatron data taking run, schedu
led to start in the year 2000. The ISL will be located in the radial region
between the Silicon Vertex Detector and the Central Outer Tracker. It will
add tracking in the forward region and significantly improve tracking in t
he central region. Together with the SVX II, the ISL forms a standalone, 3D
silicon tracker. In this article we present the design of the ISL and the
current status of its construction. (C) 1999 Elsevier Science B.V. All righ
ts reserved.