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The Extremely Large Telescope (ELT) is a 39-meter optical telescope under construction in the Chilean Atacama desert. The optical design is based on a five-mirror scheme and incorporates adaptive optics. The primary mirror consists of 798 segments. Scientific first light is planned by the end of 2027. The status of the project is described in [1]. The major challenges for the control of the telescope and the instruments are in the number of sensors (~25,000) and actuators (~15,000) to be controlled in a coordinated fashion, the computing performance and low latency requirements for the phasing of the primary mirror, performing adaptive optics and coordinating all sub-systems in the optical path. Industrial contractors are responsible for the low-level control of individual subsystems and ESO for the development of coordination functions and control strategies requiring astronomical domain knowledge. In this paper we focus on architecture and design of the High-Level Coordination and Control (HLCC). It is the component of the control software responsible for coordination of all telescope subsystems to properly perform the activities required by scientific and technical operations. We first identify the HLCC context by introducing the global architecture of the telescope control system and by discussing the role of HLCC and its interfaces with the other components of the control system. We then analyze the internal architecture of the HLCC, and the primary design patterns adopted. We also discuss how the features identified from the requirements and the use cases are mapped into the design. Finally, the timeline and the current status of development activities are presented.
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