Howard, Thank you for taking on the task of shaping up the interface. That activity is of great importance. A few comments. explicit scoped_lock(mutex_type& m); scoped_lock(mutex_type& m, detail::defer_lock_type); scoped_lock(mutex_type& m, detail::try_lock_type); scoped_lock(mutex_type& m, const elapsed_time& elps_time); The problem (as I can see it) with the set above is that "deferred", "tried" and "timed" appear to be alternatives or mutually exclusive. However, "deferred" and, say, "try" functionalities are orthogonal. That is, as one might need to defer a blocking lock scoped_lock l(m, deferred); one might need a deferred try_lock as well. Therefore, as we are trying to provide one universal lock, it appears we have to have something complex like basic_lock(mutex_type&, const elapsed_time&, defer_type); that would address all the lock variability/configurability. Such a basic lock would not be for general consumption but rather the basis for something like: try_lock : private (?) basic_lock { ... try_lock(mutex_type& m, deferred d) : basic_lock(m, 0, d) {} } Best, V.