An SLA (Service Level Agreement) is a contractual agreement between a service provider and a customer on measurable performance metrics. Typical contents include availability guarantees (e.g. 99.9%), response times for incidents, maintenance windows, and escalation paths. SLAs create transparency and a shared set of expectations. In an ISMS, SLAs are especially relevant for cloud services and IT outsourcing because they form the basis for monitoring supplier performance. You should evaluate SLAs regularly and demand corrective action when targets are missed.