The CONEX architecture for complex process control has been designed in order to cope with some control problem in the process industry. This architecture allows the integrated operation of several control layers, ranging from direct PID-based control to model based intelligent control. The architecture is organized following the principle of increasing precision with decreasing intelligence, but has a integration schema based on a multiresolutional model of the process. This is a distributed architecture based on a message passing schema between control objects. This objects have a loosely coupled operation, enhancing the reliability of the overall system. This architecture is oriented towards control in complex process plants, where the correct operation -security, quality, throughput-of the system requires the use of knowledge form operators and process engineers. Nowadays an application of this architecture is under development for a cement kiln facility in Spain.