As an owner of two 9mm and one .357sig pistols let me state my views. For civilian self-defense under the most common situations 9mm is sufficient to stop the threat. However, there are certain circumstances where 9mm falls short of what's required and that's why the search for a better service caliber began. Highway Patrol, Air Marshals, Secret Service, State and Federal Conservation Agents, urban/rural police departments, ... they're issued calibers (.40 S&W/.357sig) that have proven capable of overcoming most of these "certain circumstances". I have no way of proving it, but I believe 10mm would be a popular law enforcement choice in many jurisdictions --- except for the ever-present ACLU-type interest groups who'd sue after every OIS on the grounds of premedited intent to kill. I suspect many of the large metropolitan police departments who have not stepped up from 9mm have a long history of lawsuits and don't want to make things even more difficult for themselves. For those agencies who have adopted more powerful calibers than 9mm I have read nothing in the way of regret for having done so. Quite the opposite, if anecdotal evidence offered by LEO forum thread participants is believable. The articles by Mas Ayoob, based upon his interviews with LEO personnel and ballistics researchers, support the "street cred" of .357sig. If I remember correctly, Mas Ayoob's personal choice of sidearms is .45ACP so I see no reason for anyone to question his input. If I could have only one pistol from the ones I own I'd choose the .357sig.