One of the main objectives of the Space strategy for Europe is to foster a globally competitive and innovative European space sector, in particular by improving support to technological maturation for sub-systems, equipment and technologies, including in-orbit demonstration and validation activities, to reduce time to market. To ensure the European Union non-dependence and competitiveness in technologies, there is a clear need for a regular, sustainable, cost-effective and responsive In Orbit Demonstration/Validation (IOD/IOV) service in the European Union. Space flight heritage in real conditions and environment is often required to de-risk innovations such as new technologies, products, concepts, architectures, and operations techniques are they for unique or recurrent, institutional or commercial missions. On 31 March 2023, the European Commission issued a Call for Expression of Interest for In Orbit Demonstration/Validation of Experiments Needing Aggregation, open until 15 March 2027 with multiple cut-off dates. The objective is to promote European competitiveness and non-dependence by offering flight opportunities through IOD/IOV for European Experiments. The European Commission pre-selects on a regular basis a number of Experiments that may fly with the Horizon Europe In-orbit Demonstration/Validation (IOD/IOV) Service. The SmallSat Project 2026 will provide the Horizon Europe In-orbit demonstration/Validation (IOD/IOV) service with a Carrier based on European SmallSat platforms, with a system total mass (including experiments) in the range of 250 kg. The SmallSat Project 2026 Contractor will be responsible for specifying and delivering all elements required to accommodate a set of experiments selected by the European Commission, in order to bring them into space and to allow for demonstration and/or validation purposes. These activities include: - system studies, at ground and space segments levels, including accommodation analysis of the IOD/IOV Experiments on the IOD/IOV Carrier and the compatibility analysis with the available launch solutions, - input to the launch mission analysis for the launch services provider, - manufacturing, assembly, integration and test of the whole IOD/IOV spacecraft based on EU manufactured solutions including the selected experiments, - ground segment capabilities (facilities and operators) to operate the IOD/IOV mission, - management of interfaces between the different IOD/IOV Experiments and the IOD/IOV Carrier, - inputs to launcher interfaces, - transport and delivery of the IOD/IOV spacecraft to the Launch Site, - launch campaign, - launch and Early Orbit Phase (LEOP), - operations of the IOD/IOV spacecraft for maximum one year taking into account the specific needs of the experiments, - delivery of the experiments in-flight data to the experiment providers, with a right to use for ESA and EU, - decommissioning of the IOD/IOV spacecraft at the end of the operations. This project is funded by the European Union. ESA is the Contracting Authority and runs the procurement under the ESA/REG/001 rev.5 adapted as per the signed FFPA Agreement.