Connected and Autonomous Vehicles (CAV) are emerging due to the recent advancement in various transportation technologies. These technologies rely heavily on wireless communication to exchange significant information with each other and neighbouring vehicles. Therefore, ensuring security to these vehicles is extremely important. However, wireless communications are susceptible to various attacks including false data injection, Denial of Service, Replay attacks, to name a few. These attacks pose severe threats to CAV vehicles as they can disrupt their normal operation. To this end, securing such vehicles from attacks is foremost important. In this talk, we will focus on two major aspects: (1) How to perform Threat Analysis and Risk Assessment to identify attacks with highest risks, and (2) How to ensure security to CAVs using trust management techniques.