ECSAM is a requirements engineering and modeling method for computer-based systems (CBS). It is practiced and enhanced since 1980 by large numbers of systems and software engineers. ECSAM was developed in part at Israel Aircraft Industries for the analysis and design of complex reactive embedded systems and software. ECSAM guides the developers in systematic analysis and modeling of systems being developed and describing those using three consistent views; its conceptual architecture, operating modes, and system's capabilities. Each capability is further analyzed and described as a dynamic process. Using ECSAM it is possible to generate systematically the system?s use cases and the resulting operational scenarios. The modeling technique is applicable in the analysis of systems and any level of subsystems. The method guides the developer in the derivation of the system requirements and their systematic allocation to and association with the model's elements at the respective levels. ECSAM was the prime motive for the development of the Statecharts technology developed by Prof. David Harel as part of the method. The paper provides an overview of the ECSAM method, which is described in detail in a book that will be published in 2004 [Systems Modeling Requirements Specification Using ECSAM: Embedded Computer-Based Systems Analysis].