Retrofitting has in recent years become established as a major field of activity within the steam turbine industry. Third party upgrades by non-OEM suppliers are frequently part of the scene in these days of modern technological advancement. The main drivers for upgrading of this type are improved performance with reduced emissions, increased reliability overcoming emerging type faults and minimized maintenance for the rest of the life of the plant. The practicability in timing of manufacture and installation of a retrofit module, such as a turbine inner cylinder block, is linked intrinsically with the operation of the existing plant and to the outage schedules of each of the units. These plans may extend over a number of years. The evaluated worth of a proposed project is often decided by how quickly, within the remaining life of the overall unit, the retrofit can be supplied to start generating extra revenue. The delivery constraint of hitting an outage window adds a distinctly different aspect compared to the normal supply of a new machine. Time is required to survey the existing equipment, then design and manufacture — with minimum practical times to obtain rotors and casings, followed by shipment, installation, commissioning and testing — all required to match the date and duration of a planned outage. The whole process demands some expertise and close cooperation with plant operator is needed to ensure the optimum solution. Practical examples are discussed to illustrate the challenges involved with turbine retrofitting within specified timeframes and notable achievements are highlighted.