Floors have two fundamental structural functions in buildings: (i) transferring the vertical loads (that they are subjected to) to the vertical load bearing structures, and (ii) acting as diaphragms in the overall lateral load resisting system. In this Chapter the focus is on the former function, concentrating especially on their out-of-plane behaviour. To this aim, there are in fact various floor systems that can be used in taller timber buildings (TTBs). Among other aspects, the choice of the suitable floor system for a particular timber building depends widely on several influencing parameters, such as the span, the assigned loads, the requirements of the floor for the intended use, and the floor layout. The floors are subjected to various loads, and their design is very often governed by serviceability aspects, such as static deflections and dynamic responses (e.g., vibrations). A robust assessment of the serviceability performance requires the evaluation response of the floor system to the imposed loads, and the application of corresponding design criteria (in the region the building is situated in). In this section, aspects such as different floor systems, relevant loads, mechanical behaviour and serviceability criteria in different regions shall be discussed.