There are so few judicial opinions dealing with open source licenses that any single one is of great interest, but the pro-open source ruling of the Court of Appeals for the Federal Circuit in Jacobsen v. Katzer, No. 2008-1001 (Fed. Cir. Aug. 13, 2008) easily goes to the top of the charts of this small category. This is a highly significant opinion that will greatly bolster the efforts of the open source community to control the use of open source software according to the terms set out in open source licenses.