This paper is divided into two parts. In the first part, I extend the traditional definition of lying to illocutionary acts executed by means of explicit performatives, focusing on promising. This is achieved in two steps. First, I discuss how the utterance of a sentence containing an explicit performative such as “I promise that Φ ” can count as an assertion of its content Φ . Second, I develop a general account of insincerity meant to explain under which conditions a given illocutionary act can be insincere, and show how this applies to promises. I conclude that a promise to Φ is insincere (and consequently a lie) only if the speaker intends not to Φ , or believes that he will not Φ , or both. In the second part, I test the proposed defin...