We have used a combination of optical absorption spectroscopy, 21 cm HI mapping, and millimetric CO mapping, to explore the fine structure of the ISM clouds within 200 pc of the sun. We find examples of molecular cores within cold atomic clouds, cold atomic clouds within warm ionized clouds, and warm ionized clouds without cold cores (using velocities as identifiying tags). Cold clouds of up to a couple of thousand solar masses, and warm clouds of up to a few hundred solar masses are found. We explain our three-dimensional mapping procedure, and compare our results with the predictions of the best known model scenarios for the structure of the ISM.