Sidney Sax (1913–2005) was a British violinist. He was a noted orchestral leader and also a contractor, arranging personnel for many recording sessions. In 1964, he jointly founded the National Philharmonic Orchestra, London together with Charles Gerhardt.
The National Philharmonic Orchestra, which was later incorporated in 1970, was a freelance orchestra that included amongst its players leading musicians from all the London orchestras. Sax had often contracted the leaders of most of London's orchestras to populate his first violin section.