Bryan Boreham, a Distinguished Engineer at Grafana Labs, explores the intricacies of PromQL, the query language for Prometheus, aiming to provide a comprehensive understanding of how it processes queries. Despite being a Prometheus maintainer, Boreham found many aspects of PromQL obscure, prompting him to delve into its mechanics and share his insights at PromCon 2024. PromQL is crucial for expressing which metrics to use and operations to perform, typically for dashboard visualization, with two primary query types: instant and range. The execution of a PromQL query involves parsing text into an Abstract Syntax Tree (AST), which the engine processes to pull data from storage, employing selectors, functions, aggregations, and operators to compute results. Boreham discusses the internal workings of PromQL, including how data is fetched, processed, and output, along with the tools and resources available for learning and optimizing queries. He emphasizes the role of PromQL functions, aggregations, and binary operators, and how they interact to perform complex data manipulations, while also highlighting the significance of tracing and profiling for gaining deeper insights into query execution.