States typically seek to attract foreign investments to establish large-scale projects that drive national economic growth. One of the key methods to encourage private foreign entities to invest and enter into long-term contracts with the state is by offering guarantees that create a suitable environment for foreign investments. Among the most significant of these guarantees is the principle of legislative stability, also known as legal stability, which obligates the state not to amend the laws governing international contracts concluded with private foreign entities or to prevent subsequent legislative amendments from applying to these contracts. The principle of legislative stability may be either voluntary or legal, and its effects vary depending on its source. A voluntary legislative stability clause subjects the contract to material rules, thereby exempting it from the authority of national laws. Conversely, legal legislative stability does not affect the legal status of the applicable law, ensures legal security, upholds the legitimate expectations of the parties, and maintains the legal nature of the applicable law. However, it is considered less encouraging for foreign investors.