FieldTrip is Open Source software and you can use it freely under the GPL license without other restrictions. However, we do appreciate getting acknowledged for the contribution of our project to your research. Please note that your references to FieldTrip also help us to ensure continued funding for the FieldTrip project, code development and support.
If you have used FieldTrip for the analysis that you are reporting on in a scientific publication, we kindly ask you to refer to the following publication
Publications that are referring to FieldTrip are listed here.
Publications that describe (some of) methods that are implemented are listed here.