Stereolithography (SL) technology, which is the oldest Additive Manufacturing technologies, is gaining momentum in the prototyping world thanks to its new materials exhibiting thermoplastic-like performances. This additive fabrication process not only allows for intricate part designs but also delivers functional prototypes, which eases concept part testing. Design engineers now save a huge amount of time when they test a design concept. Not so long ago Stereolithography SL resins were much too brittle to allow for e.g. evaluating the impact resistance of a prototype. Thanks to the many advances of Additive Manufacturing technologies, and thanks to the significant reduction of the time-to-market they bring to part designers, the also-called Rapid Prototyping industry is growing fast and reached US$ 1.1 billion in 2009.With an annual growth of more than 20% and benefiting from further technical advances on materials, the Rapid Prototyping and Rapid Manufacturing technologies will show even more in the next decades. A new wave of opportunities has already spread into this fast growing industry: the production of short runs. AM technologies in general, and Stereolithography in particular, are now more than ever used to produce a limited number of parts, even when it deals with e.g. complex design of spare parts. The injection molding of plastic parts is not competitive when only a few parts are needed because the steel mold cannot be amortized. This is one of the reasons why the AM technologies including Stereolithography technologies are well suited for the aerospace industry. For the same reason the medical sector is also widely using stereolithography and the other Rapid Prototyping and Rapid Manufacturing technologies. Because every patient is unique, dental implants and other hearing aids will always be produced on demand, and drawings will change from one patient to another.Even though the SL technology is making progress in handling short runs and producing limited amount of spare parts, it is still mainly used in the prototyping world. Following T. Wohlers, a renowned and well-known expert in the AM technologies, there are roughly 70% of parts using AM technologies being sold as prototypes or unique models1. Despite the growing interest towards the manufacture of tailor-made parts there were also some key advances made these past years on materials to improve the performances of prototypes. It is now easy to get functional prototypes. Resin producers developed special resins for AM technologies to make them closer to the serial production resins - even if these AM resins will never be the exact offset of injection molding grades experts now talk of e.g. ABS-like properties materials. Other AM resins were also developed to increase heat resistance or improve transparency. All these improvements were conducted to allow functional testing. It is not only possible to quickly get a complex 3D shape plastic part in hand quickly. It is also possible to assess the functional design.Some of these SL resins are even USP Class VI approved, which is of great help when OEMs and device manufacturers develop medical functional prototypes. From the prototypes to the first tens of parts, which will go through severe functional testing procedures, the use of medical approved resins makes the transition very easy. These material advances help to speed-up the development phase and bring more flexibility to part designers and part development project managers.