Zimmermann, Reinhard MPI for Comparative and International Private Law, Max Planck Society;
https://max-eup2012.mpipriv.de/index.php/Principles_of_European_Contract_Law_(PECL) (Any fulltext)
Zimmermann, R. (2012). Principles of European Contract Law. In J. Basedow, K. J. Hopt, & R. Zimmermann (Eds.), The Max Planck Encyclopedia of European Private Law (pp. 1325-1328). Oxford: Oxford University Press.