With the growth of wireless and mobile technologies, we are witnessing an increase in location-based services (LBS). Although LBS provide enhanced functionalities, they open up new vulnerabilities that can be exploited to cause security and privacy breaches. Specifically, location data of individuals that are used by such services must be protected from security and privacy breaches. Such services will require new models for expressing privacy preferences for location data and mechanisms for enforcing them. We identify the factors on which location privacy depends and propose a scalable model for expressing privacy that can be used for LBS and other applications where the privacy of location information must be protected. Categories and Subject Descriptors K.6.5 [Management of Computing and Information Systems]: [Security and Protection] General Terms Access control, privacy Keywords Location privacy