  The Square Kilometer Array (SKA) represents the next major, and natural, step
in radio astronomical facilities, providing two orders of magnitude increase in
collecting area over existing telescopes. In a series of meetings, starting in
Groningen, the Netherlands (August 2002) and culminating in a `science retreat'
in Leiden (November 2003), the SKA International Science Advisory Committee
(ISAC), conceived of, and carried-out, a complete revision of the SKA science
case (to appear in New Astronomy Reviews). This preface includes: (i) general
introductory material, (ii) summaries of the key science programs, and (iii) a
detailed listing of standards and assumptions used in the revised science case.
