Which is the best cut of beef to make a stew?

All our supermarkets sell 'stewing beef' but none of them state what part of the animal it is from or give any instructions these days. Some of this beef is tough as can be. If I go to an actual private butcher what should I ask for to be sure it will be right for the job. I don't want to just ask for stewing beef or he, also, might just sell me what he want to get rid of. I want to sound knowledgeable when I go there, even though I am not.