The disclosure generally relates to negotiating a best device-to-device (D2D) radio access technology (RAT) to use in a D2D connection. In particular, two wireless devices that correspond to potential D2D peers may exchange respective radio configurations according to a D2D coexistence protocol to mutually negotiate the “best” RAT to use in the D2D connection, wherein the exchanged radio configurations may comprise at least radio capabilities and coexistence states (e.g., in-device and/or cross-device coexistence states) associated with the respective wireless devices. The potential D2D peers may then negotiate one or more compatible RATs that are available to use in the D2D connection according to at least the radio capabilities and the in-device and cross-device coexistence states exchanged therebetween. As such, the two wireless devices may then establish one or more D2D connections using the negotiated compatible RAT(s).