The Australian Opera and Ballet Orchestra (based in Sydney, New South Wales, Australia) is one of two full time, permanent orchestras employed jointly to provide music for Opera Australia and The Australian Ballet, the other is known as Orchestra Victoria (based in Melbourne). The orchestra (and its Victorian cousin) was formerly known as The Elizabethan Sydney Orchestra and The Elizabethan Melbourne Orchestra respectively. It was initially established by the Australian Elizabethan Theatre Trust.
This orchestra provides musical accompaniment to the two above mentioned arts bodies and one few opera orchestras in the world that operates in a repertory style of operation. Meaning, that its performances are not set in blocks (like many European opera houses) rather, Opera Australia's seasons produce four or five operas simultaneously. Other opera houses that operate like this are The Metropolitan Opera, New York. The Royal Opera House, Covent Garden, London and La Scala, Milan.