Publisher Summary This chapter discusses the motivations, development process, technical architecture, and examples of the Computer Aided Process Engineering (CAPE)-OPEN Standard. The CAPE-OPEN (CO) standard was developed in two successive EU-funded projects, CAPE-OPEN and Global CAPE-OPEN (GCO). The CO project brought together software vendors, global chemical manufacturing companies and universities to solve enterprise software for designing and optimizing process plants could be made interoperable. The CO standard is characterized by a unique and global version number, and is described by a set of documents. CO and GCO relied on a structured process starting from user's requirement and leading to software implementation, test and validation. The process is incremental and uses Unified Modeling Language (UML) notation for use case diagrams, sequence diagrams, component diagrams and class/interface diagrams. The elements of the standard: its development process; its global architecture, an example of use for unit operations and physical properties; and a further look at other portions of the standard, namely numerical solvers and access to physical properties data bases are focused.