I'd like to restart the discussion on how conversions will work in Boost.Python v3. Here's the starting point: I'd like to see support for static, template-based conversions. These would be defined by [partial-]specializing a traits class, and I tend to think they should only be invoked after attempting all registry-based conversions. Users would have to include the same headers in groups of interdependent modules to avoid specializing the same traits class multiple times in different ways; I can't think of a way to protect them from this, but template-based specializations are a sufficiently advanced featured that I'm comfortable leaving it up to users to avoid this problem. We've had some discussion of allowing different modules to have different registries (in addition to a global registry shared across modules). Leaving aside implementation questions, I have a little survey for interested parties: 1) Under what circumstances would you want a conversion that is completely limited to a specific module (or a group of modules that explicitly declare it)? 2) Under what circumstances would you want a conversion to look in a module-specific registry, and then fall back to the global registry? 3) Considering that we will have a "best-match" overloading system, what should take precedence, an inexact match in a module-specific registry, or an exact match in a global registry? (Clearly this is a moot point for to-Python conversion). Finally, can anyone give me a reason why having a global registry can lead to a violation of the "One Definition Rule"? This was alluded to many times in the earlier discussion, and there's no doubt that a global registry may lead to unexpected (from a given module's perspective) behavior - but I do not understand the implication that the global registry can result in formally undefined behavior by violating the ODR. Thanks! Jim