With the development of information and communication technology (ICT), car sharing becomes more and more popular. It is a short-term car rental service and Volvo entered this market in 2019. The purpose of this thesis is to design for a seamless and personalized experience for car sharing users with the smartphone.

A literature overview and user interviews were performed to get a general understanding of the user groups, usage patterns of the car sharing service and their experience of connecting the smartphones to the car. Two user tests were made to iterate the design and get to know users’ opinions about the design concepts. Personas and scenarios were built up and that made the basis for the design of user interfaces on the car-sharing apps and the \ac{IVI}. As a result, a concept solution was brought up. The general process of the car sharing service was: booking a car, finding a car, getting onboard, picking up friends, and getting offboard. For drivers, they can find and unlock the car seamlessly with the phone, get onboard with all preferred settings applied, safely log into the IVI system, easily pick up friends by seeing their position, and clear personal data when they return the car. For passengers, they can see the position of the car and estimated arrival time, scan a QR code to turn their phones to a remoter of the IVI system, directly send a destination to the IVI system, and share their favorite music. Nearly all the users liked the designed functions in the tests but the adoption of the service was mainly affected by two factors. One was privacy concerns and the other was function value. Users made a choice of how important more functions were compared with sequences regarding loss of privacy. More future research needs to be done to further validate the findings of this thesis and achieve the designed experience.