This is not an all-inclusive list. I have on this trip enjoyed operas in Mannheim and Hamburg, but over a lot of performances in recent years the specific companies named hold up. I would always have listed the Royal Opera, Covent Garden, in London, on any previous list. But until its new house opens, the company is touring and seems to be exhibiting varying quality. Formal dress is required in no opera house, and you will find in almost every theater a fair number of younger people in shirts and blue jeans.
Tuxes are rarer than in most U.S. houses.
You can often buy tickets when you get to the city although it is smart to book from the States for London, Paris, and Berlin. They are comparable to large American company prices. For the opera traveler, or any traveler for that matter, one of the pleasures of modern life can be his or her laptop computer. The virtues are that you are in instant, cheap communication with anyone anywhere via E-mail. Phone calls from Europe from hotels are ruinously expensive.