These recommendations present a guide to the design of two-way spanning, post-tensioned concrete flat slabs using unbonded or bonded tendons. Recommendations purely related to the use of unbonded tendons are clearly marked. These recommendations are intended only for the design of post-tensioned flat slabs in buildings and do not include the use in bridges. Post-tensioned concrete construction can be defined as unbonded or bonded, depending on whether the tendon ducts are filled with a cement grout (in order to provide a bonded structure) or whether the tendons are suitably coated and wrapped or greased and plastic covered (unbonded). While in a number of countries, (e.g., United States and Canada) economic and construction considerations have resulted in the selection of unbonded tendons, in other countries the use of the traditional bonded tendons is favoured, (e.g., Australia). Some of the advantages claimed for the use of unbonded tendons can be summarized as follows: Extremely low friction values, tendons are fully protected against corrosion during construction, maximum possible tendon drape due to the small diameter of the tendon; this is of major importance in slender structures such as flat plates, simple and fast placement of the tendons, avoidance of grouting operations. When tendons are grouted after stressing the claimed advantages are particularly that the bond between the concrete structure and the tendons increases the ultimate strength and less reliance is placed on the long-term adequacy of the anchorage.