The quality of music you'll be able to access through the service will depend on the connection and equipment you own, with MP3 download options on offer for those unable to support lossless files.
Features of this new service include an "intuitive search engine" designed especially for classical music, and liner notes, libretti and composer/artist information on most recordings.
Naxos says ClassicsOnline HD-LL is the first lossless music streaming service to launch worldwide and use "adaptive bitrate streaming technology", with both streaming and downloads available.
Album downloads are available in FLAC, ALAC, WAV, AIFF or MP3 formats, while you can listen to streamed tracks via a desktop computer or on your mobile device.
Naxos founder Klaus Heymann said: "[ClassicsOnline HD-LL is] proof of our commitment to making a wide range of classical music available in state-of-the-art sound with a sophisticated search capability."