This course deals with the concept of acoustic comfort in closed spaces and its three key components, i.e. optimal room acoustic conditions, adequate sound insulation from neighbouring spaces, and maximum allowable level of noise generated by internal sources located in the room itself. The concept of acoustic comfort is then linked to appropriate architectural design steps that need to be planned and implemented, if optimal level of acoustic comfort is to be achieved in the designed/refurbished space, regarding its size and intended purpose. The specifics of various types of closed spaces are considered in the context of acoustic comfort, and the corresponding requirements set on general-purpose, special-purpose, and technological spaces are defined. Methods of protection from noise emissions and immisions are discussed, as well as the appropriate architectural and building constructions that provide adequate level of protection. In the room acoustical sense, the sound field in closed spaces is considered, as well as the influence of early and late reflections on the sound field in rooms. Architectural design measures are considered that can be implemented in order to manipulate the quantity of early and late reflections in the overall impulse response of the room, as well as the consequences of such design manipulations. The course of the process of acoustic design of a closed space is laid out, the goal being the achievement of optimal acoustic comfort according to all three above-mentioned criteria. This includes the definition of the project task and the approaches used in the acoustic design process. Special attention is put on the differences between different methods used for calculating relevant room acoustical parameters, and the advantages and limitations of different methods are discussed.