Before a performance, which note do orchestras traditionally tune up to?

Orchestras always tune to 'A', because every string instrument has an 'A' string. The standard pitch is A=440 Hertz (440 vibrations per second). Some orchestras favor a slightly higher pitch, like A=442 or higher, which some believe results in a brighter sound. If you ever played in concert band, you'll remember that you always tuned to B flat. This is because most of the band instruments are actually pitched in B flat, and so this is their natural tuning note.