This document analyzes whether proprietary software that interacts with open source software needs to be distributed under an open source license as well, focusing specifically on the GNU General Public License (GPL). It discusses how copyright law considers a work to be a derivative if it is substantially similar to pre-existing copyrighted work. It examines guidance from GPL authors and the Oracle v. Google case to determine what constitutes copying for GPL purposes. The document concludes by recommending companies implement processes to review code for open source license compliance before distribution.