My rule of thumb - subject to change for tough international situations - is that an hour transfer is tight but perhaps doable IF both flights are on the same airline and same itinerary. Same terminal also enters into the equation. In some cases, a change from one airline to another in the same alliance might also be ok if in the same terminal.

For changes that involve different, unrelated airlines, different terminals or separate tickets/itineraries and international connections, an hour is just not enough time.