If you use results obtained with EasySpin in any scientific publication, cite
Stefan Stoll, Arthur Schweiger
EasySpin, a comprehensive software package for spectral simulation and analysis in EPR
J. Magn. Reson. 178(1), 42-55 (2006)
[pdf file]
Stefan Stoll, Arthur Schweiger
EasySpin: Simulating cw ESR spectra
Biol. Magn. Reson. 27, 299-321 (2007)
[pdf file]
EasySpin: Software for Electron Paramagnetic Resonance
Lecture slides,
4th International EPR Summer School,
St. Andrews, Scotland, August 2008
[pdf file]
Other articles about about spectral simulation in EPR and the algorithms used in EasySpin are cited in the above articles.