In this chapter, we survey, systematize, and evaluate different approaches to the statistical estimation of resource demands based on easy-to-measure system-level and application-level metrics. We consider resource demands in the context of computing systems; however, the methods we present are also applicable to other types of systems. We focus on generic methods to approximate resource demands without relying on dedicated instrumentation of the application. The goal is to estimate the resource demands based on indirect measurements derived from commonly available metrics (e.g., end-to-end response time or resource utilization).