In the field of microwave engineering, additive manufacturing technologies enable the rapid prototyping of cost-effective and light-weight components and the simple realization of otherwise impractical topologies. In this work, a technique for the creation of passive microwave components based on 3D printing of plastic material is discussed. A number of devices are presented, including a microstrip-to-waveguide transition, a dielectric sensor, and two microwave filters. Each of these components highlights the aspects that additive manufacturing can bring to their respective applications.