The trial, in San Francisco federal court, is due to start this afternoon or tomorrow, after a deadline passed on Friday for the companies to reach a settlement.
Oracle's accusing Google of infringing various Java-related patents and copyrights with its Android technology, which it wants made compatible with the rest of Java.
It's demanding royalties, and is expected to ask for as much as $1 billion. It was originally hoping for much more, but has had to reduce its claims after five of the seven patents in question were invalidated.
According to Oracle, Google copied 37 Java API design specifications and implementations, along with 11 Java source code files.
Google, though, is claiming that because Java is open source, Oracle has no right to enforce the copyrights.
Of the the two patents remaining in the case, one, covering a way of compiling and interpreting code, has already had a preliminary rejection from the Patent Office. The other covers a method of generating code.
The trial's expected to take about eight weeks, with evidence coming from the two Larrys - Oracle CEO Ellison and Google CEO Page - are expected to give evidence early on. Copyright will be dealt with first, with the patent disputes following.
The trial could set a precedent as to whether APIs are copyrightable, with significant implications for developers. If they are, developers could be forced to create new versions of existing products.