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abstract: 'The fact that both the D6-brane and the orientifold 6-plane have smooth, horizon-free descriptions in M-theory makes them especially useful in understanding certain aspects of brane physics. We briefly review how this connection has been used to understand a number of effects, several of which are associated with the Hanany-Witten transition. One particular outcome is a “confinement mod 2” effect for zero-branes in the background of a single D8-brane. We also discuss an interesting puzzle associated with flux-expulsion from D6-branes in this context. Finally, we discuss the promise of using a similar M-theoretic description of the orientifold 6-plane to understand the consistency of stringy negative energy objects with the 2nd law of black hole thermodynamics.'
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**The Past, puzzles, and promise of 6-branes**

Donald Marolf

Physics Department, Syracuse University, Syracuse, NY 13244

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Introduction
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This outline for this talk arose in an attempt to find a strong enough unifying theme in my recent work to keep an audience’s interest throughout a 50 minute talk. Rather to my surprise, such a theme did exist and, not only did it run through quite a bit of my recent work, but it continues to run through planned future work as 