Currently there is significant and increasing demand for quick data storage and access any time. Storage is a fundamental need and Cloud environments accomplish this. The evolvement of the IT technologies offers the user to a large variety of useful services. In order for the user to have a guarantee for these services SLAs are signed. In this paper, we present an SLA Management mechanism for Cloud environments. SLA enforcement is based on rules that are updated in runtime in order to proactively detect possible SLA violations and handle them in an appropriate manner.