This paper addresses the need for a formal specification method for real-time systems, which are characterized by quantitative timing properties. The authors classify these properties into five categories: maximal distance between an event and its reaction, exact distance between events, minimal distance between events, periodicity, and bounded response time. Standard temporal logics cannot handle these quantitative requirements, so the paper proposes an extension called *metric temporal logic*. This extension includes a distance function to measure time and introduces metric temporal operators that can express the five types of quantitative timing properties. The paper illustrates the application of metric temporal logic through several examples involving real-time features such as time-outs and wait/delay statements. The structure of the paper includes an introduction, a discussion of real-time systems, a review of temporal logic, the introduction of metric temporal logic, examples of its application, and conclusions.This paper addresses the need for a formal specification method for real-time systems, which are characterized by quantitative timing properties. The authors classify these properties into five categories: maximal distance between an event and its reaction, exact distance between events, minimal distance between events, periodicity, and bounded response time. Standard temporal logics cannot handle these quantitative requirements, so the paper proposes an extension called *metric temporal logic*. This extension includes a distance function to measure time and introduces metric temporal operators that can express the five types of quantitative timing properties. The paper illustrates the application of metric temporal logic through several examples involving real-time features such as time-outs and wait/delay statements. The structure of the paper includes an introduction, a discussion of real-time systems, a review of temporal logic, the introduction of metric temporal logic, examples of its application, and conclusions.