Location based services (LBS) are one of the most promising and innovative directions of convergence technologies resulting of emergence of several fields including database systems, mobile communication, Internet technology, and positioning systems. Although being initiated as early as middle of 1990's, it is only recently that the LBS received a systematic profound research interest due to its commercial and technological impact. As the LBS is related to the user's location which can be used to trace the user's activities, a strong privacy concern has been raised. To preserve the user's location, several intelligent works have been introduced though many challenges are still awaiting solutions. This paper introduces a survey on LBS systems considering both localization technologies, model and architectures guaranteeing privacy. We also overview cryptographic primitive to possibly use in preserving LBS's privacy followed by fruitful research directions basically concerned with the privacy issue.