Definition
Pacta sunt servanda (En.: agreements must be kept, Fr.: les conventions doivent être respectées, De.: Verträge sind einzuhalten)(See also: treaty, clausula rebus sic stantibus, international agreements, good faith) = international law principle according to which every treaty in force is binding upon the signatory parties. The states must perform their assumed obligations with good faith. The only exceptions of this principle are the peremptory norms of the general international law (ius cogens).
The opposite of pacta sunt servanda is the clausula rebus sic stantibus principle that allows a state to not fulfil its obligations in case of a fundamental change of circumstances.
~ (in civil law) = the contract is law between the parties; the principle symbolises the importance of a promise and the force of the mutual and accordant wills of the parties in private law.
Useful resources
Legislation
https://treaties.un.org/doc/Publication/UNTS/Volume%201155/volume-1155-I-18232-English.pdf - Vienna Convention on the law of treaties, Article 26 [English]
http://www.unidroit.org/english/principles/contracts/principles2010/integralversionprinciples2010-e.pdf - UNIDROIT Principles, Article 1.3 [English]
http://www.cdep.ro/pls/dic/site.page?den=act2_1&par1=1#t1c0s0sba10 - Romanian Constitution, Article 11(1) [Romanian]
Online publications
http://derecho-scl.udd.cl/files/2011/11/v18a05-Pablo-Rodr%C3%ADguez-Pacta-sunt-servanda.pdf - Rodriguez Grez, P. , 2008, Pacta sunt servanda [Spanish]
http://ir.lawnet.fordham.edu/cgi/viewcontent.cgi?article=2165&context=ilj - Yackee, J. W., 2008, Pacta sunt servanda and state promises to foreign investors before bilateral investment treaties: myth and reality [English]
http://razonamientojudicial.com/wp-content/uploads/2011/10/Principio-Pacta-Sunt-Servanda.pdf - Platas Pacheco M.d.C, 2014, El principio Pacta sunt servanda y la clausula Rebus Sic Stantibus; entre la contradiccion y la complementariedad; un reto logico-argumentativo [Spanish]
http://papers.ssrn.com/sol3/papers.cfm?abstract_id=2362526 - Lekkas S.I., Tzanakopoulos A., 2013, Pacta sunt servanda versus Flexibility in the Suspension and Termination of Treaties [English]
Publications
Constantin V., 2010, Drept internațional, București, Ed. Universul Juridic [Romanian]
Corten O., Klein P., 2011, The Vienna Conventions on the Law of Treaties: A Commentary, Volume I, New York, Oxford University Press [English]
Thirlway H., 2014, The sources of international law, New York, Oxford University Press [English]
Viliger M. E., 2009, Commentary on the 1969 Vienna Convention on the Law of Treaties, Leiden, Martinus Nijhoff Publishers [English]
By Raluca-Andreea Trîncă-Găvan