GNU GPL FAQ, selected entries:
- I'm writing a Windows application with Microsoft Visual C++ and I will be releasing it under the GPL. Is dynamically linking my program with the Visual C++ run-time library permitted under the GPL?
- Can I use GPL-covered editors to develop non-free programs? Can I use GPL-covered tools to compile them?
- In what cases is the output of a GPL program covered by the GPL too?
Longer reading: Transcript of one of Richard M. Stallmans speeches (the basic one with the printer-story, the story of FSF and so on).