The synthesis of radiopharmaceuticals not only requires a high level of automation to ensure repeatability of the process but also requires flexibility to account for the minute modifications required to achieve high yields on different radiolabeling processes. These partly contrasting requirements have induced the practice in the field to purchase synthetic modules and perform homemade modifications as required. In this regard, 3D printing techniques can offer unique reaction environments that can be easily modified following user needs and in fact are starting to be used in radiochemistry. This chapter provides basic knowledge on 3D printing for chemical reactors and shows the first examples of applying this approach to radiochemical reaction processes.