At this early phase in the development of microfabricated fluidic systems, only a few components or functions have been microfabricated. Some sort of interface to the remaining 'off chip' components is required. For example, a variety of analysis techniques have been demonstrated in microfabricated channels, and cells, but sample preparation is to date still mostly performed off chip, involving pipetting, tubing and titer plate interfacing. The transition from micro to macro components has been to date rather crude, consisting mostly of tubing glued into or over holes etched into silicon or glass substrates. This paper presents new, micromachinable, joining and interconnecting structures that enable the modular, plug-in assembly of fluidic components to one another, to tubing, and into a fluid channel breadboard. Micro-to-miniature interfacing elements for making connections between microchannels and standard tubing, and both horizontal and vertical channel- to-channel interconnects will be demonstrated. Excellent seals are created using photopatternable silicone O-rings that are held in compression by the connecting structure. This technology allows one to assemble a fluidic microsystem with both custom and off the shelf, micro or miniature components. The connections are all reversible, making the system design reconfigurable and components easily exchanged.