Downtown Oakland is the Central Business District of Oakland, California. It is bounded by 23rd Street to the North, the 980 freeway to the West, the waterfront to the South, and Lake Merritt to the East. There are approximately 100,000 jobs and 17,000 residents downtown. More information can be found on Wikipedia.
The City of Oakland maintains a page on downtown called MeetDowntownOak.com. The Downtown Association of business improvement districts can be found at DowntownOakland.org. Downtown can be reached by multiple AC Transit lines, Amtrak (Jack London Square), Greyhound, the Oakland/Alameda Ferry, and BART (12th and 19th Street Stations).