Quantum Plaintext Non-Malleability Jeroen van Wier Abstract: When two parties communicate they often require a certain level of security. In particular one might desire that a message cannot be altered in transit. This is called non-malleability and has been studied extensively in the non-quantum setting, but was only recently introduced in the field of quantum computing. This thesis provides two ways of defining non-malleability in the quantum setting. One of these definitions is based on previous quantum notions, and the other is an extension of a well-researched classical notion. These definitions capture different forms of non- malleability, and we provide an argument why either can be considered correct.