Service levels describe services provided to users within a given period of time in measurable terms, with SLOs (service level objectives) being the goals set for availability expected out of a system, SLIs (service level indicators) being key measurements and metrics to determine the availability of a system, and SLAs (service level agreements) being legal contracts that explain what is agreed upon and what happens if systems don’t meet SLOs. Setting the right SLOs is crucial for improving service reliability and creating an incredible customer experience by understanding user expectations and needs, analyzing historical performance, and defining specific, measurable indicators such as latency, error rate, or uptime. Consistently not meeting SLOs may indicate underlying issues in the service, requiring root cause analysis and improvement efforts. Balancing between setting aggressive SLOs and realistic ones involves understanding user expectations and technical capabilities, involving stakeholders from both business and technical sides. SLIs measure real-time user experience and represent a proportion of successful outputs for a level of service, expressed as a percentage, with examples including availability/uptime, latency, throughput, error rate, saturation, coverage, freshness, capacity, and system boundaries. Service levels come into play to help SRE teams identify critical components of their applications and infrastructure, requiring accurate, customized SLIs and SLOs based on historical system performance to set goals around the performance of a system. Service level management ensures that processes and operational agreements for services provided to customers are appropriate, including monitoring and reporting on service levels, setting and adjusting SLOs, determining SLIs, making sure SLAs are met, and holding customer reviews. Implementing good practices for SLIs, SLOs, and SLAs benefits teams with easy setup, defining reliability across teams, iterating and improving, standardizing reliability, and getting started with New Relic's service level management capabilities.