Aerojet Rocketdyne has been working with NASA to develop a way to 3D print rockets. Well, not the WHOLE rocket, but certain critical parts, namely an Injector Assembly.
They're working on a completely integrated manufacturing process with Selective Laser Melting technology that will be capable of rapidly producing "highly critical rocket engine components". We suspect they are leveraging 3D printing's ability to create complex objects that are lightweight compared to the traditional method of bolting several pieces together - which often adds significant weight.
The twist here is that they have to certify that the parts produced are truly safe to use by passing numerous tests. Part of that certification was accomplished recently by using a 3D printed part in a "hot fire test". You can imagine what that means.
The test was successful; More rocket parts will be printed.