Extreme Sailing Series

{{Infobox recurring sailing competition

| name = Extreme Sailing Series

| logo = Extreme Sailing Series logo.jpg

| alt =

| caption =

| formerly =

| replaced =

| founded = {{start date|2007|df=y}}

| organizer = OC Sport

| classes = Extreme 40 (2007–2015)
GC32 (2016–2018)

| champions = Alinghi (2018)

| most_champs = Alinghi (4)
The Wave, Muscat (4)

| website = {{URL|extremesailingseries.com}}

| footnotes =

}}

The Extreme Sailing Series (ESS) (formerly the iShares Cup) was an annual global racing series, organised by OC Sport, which ran from 2007 to 2018.

The series started in 2007 with its main attraction being the stadium racing which puts the race course inside a stadium environment for the ease of spectators' viewing.{{cite web |url=http://www.extremesailingseries.com/about-the-series |title=Inside the series |website=www.extremesailingseries.com |url-status=dead |archive-url=https://web.archive.org/web/20150112222524/http://www.extremesailingseries.com:80/about-the-series |archive-date=12 January 2015}}

Many of the sailors taking part in the series were around-the-world yachtsmen, Olympic medallists, America's Cup sailors, World and European champions and even world record holders.{{cite news|title=All Star Cast lined up for 2012 Extreme Sailing Series|url=http://www.mysailing.com.au/news/all-star-cast-lined-up-for-2012-extreme-sailing-series|access-date=7 February 2013|newspaper=mysailinr.com.au|date=17 February 2012}}{{cite news|last=Laven|first=Kate|title=Ben Ainslie faces challenge in Extreme Sailing Series|url=https://www.telegraph.co.uk/sport/othersports/sailing/8795479/Ben-Ainslie-faces-challenge-in-Extreme-Sailing-Series.html|access-date=7 February 2013|newspaper=The Telegraph|date=28 September 2011}}

The series was terminated in 2019 after the event became financially nonviable and OC Sport were unable to secure a management buy-out.{{cite news |last1=Extreme Sailing Series |title=OC Sport confirms the closure of the Extreme Sailing Series |url=https://www.sail-world.com/news/218555/Closure-of-Extreme-Sailing-Series |access-date=11 October 2019 |agency=sailworld.com |date=13 June 2019}}{{cite news |title=Era over for Extreme Sailing Series |url=https://www.sailingscuttlebutt.com/2019/06/13/era-over-for-extreme-sailing-series/ |access-date=11 October 2019 |date=13 June 2017}}