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Summary form only given. Two IC chips placed face-to-face can communicate without direct electrical contact. The capacitive coupling between their top-level metal layers can carry data. We have demonstrated such "proximity communication" on 50 μm centers and data rates similar to on-chip wires. Such communication offers attractive speed, density, and energy economy, but requires accurate mechanical alignment. Proximity communication requires sensitive amplifiers to compensate for the attenuation suffered as signals pass from one chip to the other. Signals with uncertain arrival times require an amplifier that can distinguish between signal and no signal. The difference between receiving attenuated data signals and receiving attenuated control signals focuses attention on the fundamental problem of time in asynchronous systems. This talk addresses the above issues.