Blue Planet II is a 2017 British nature documentary series on marine life produced by the BBC Natural History Unit. Like its predecessor, The Blue Planet (2001), it is narrated and presented by the naturalist Sir David Attenborough.

Blue Planet II was announced in 2013 and was filmed over four years in 39 countries, in more than 125 international trips. The score was composed by Hans Zimmer, Jacob Shea and David Fleming. The rock band Radiohead reworked their 2011 song "Bloom" with Zimmer for the series.

Blue Planet II debuted on 29 October 2017 and was simultaneously cast on BBC One, BBC One HD and BBC Earth, making it the first natural history series to premiere on the same day in the UK, Nordic regions, Europe and in Asia. In the US, it premiered on January 20, 2018, as part of a five-network simulcast on BBC America, AMC, IFC, Sundance, and WE tv.

Blue Planet II received acclaim. It had the highest viewing figures of any television programme in the UK in 2017, and was so widely watched in China that it reportedly caused internet problems. It is credited with increasing public and political interest in issues affecting marine life, in particular marine plastic pollution, which was dubbed "the Blue Planet effect".