One can observe that more and more companies are focusing on their core compenetency and are outsourcing parts or even complete business processes to service providers. Service Level Agreements (SLAs) are used as a contractual basis to define certain non-functional properties (e.g. response time) a service has to provide. To determine the SLA of a business process a priori, the SLAs of the invoked services need to be aggregated into a single SLA for the business process. This paper defines a method how a service provider can aggregate the SLAs of the individual services within a business process into a single SLA. This provides a service provider with the capability to annotate the service that the business process implements with an appropriate SLA. We propose a framework that helps in carrying out the SLA aggregation within business processes. The framework consists of two parts: (i) a formal model for SLAs and (ii) a concept to aggregate SLAs, where algorithms can be plugged in.