Abstarct: In this thesis a cooperative scheme for secure device to device (D2D) communications underlaying cellular networks is proposed. In our scheme the cellular baxse station (BS) wants to transmit its information to cellular user (CU). Meanwhile, two devices want to communicate using the same spectrum used by cellular network. We consider two different system model in our thesis. In first system model, device to device users communicate directly with the help of some decode-and-forward (DF) relay nodes. In addition there exists a malicious user which wants to eavesdrop on information transmission of D2D pair. In seconde system model, device to device users communicate directly with the help of an untrusted amplify and forward (AF) relay node. We consider the signals received from both the direct lixnk and relay lixnk for both system models. In two system model, the transmit power of the transmitter of D2D pair and the relays is limited such that the outage performance of cellular network is satisfied. We study the performance of two proposed system model, which is measured baxsed on the secrecy outage probability, and obtain the closed form exxpression for the secrecy outage probability. Finally, the performance of the two proposed system model is evaluated using simulations.