A brand new tournament has kicked off the 2023 summer of tennis in Australia, with the United Cup replacing the ATP Cup.
National teams are going toe to toe, as some of the sport's biggest names compete in the mixed warm-up event ahead of the Australian Open.
The Sporting News takes you through all the key details for the tournament.
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What is the United Cup?
The United Cup is a new mixed tennis tournament, played in a team competition format.
In 2023, 18 nations - comprising up to four men and four women - are facing off to be crowned inaugural champions.
Countries have been split into six pools of three teams, with semi-finals and a final in Sydney to cap off the event.
Teams will play four singles matches (two men's and two women's) and one mixed doubles match in the round-robin stage.
There is a US$15 million (AU$22 million) prize pool on offer, so is plenty of incentive for players to participate in the warm-up event.
When and where is the United Cup?
Whilst the ATP Cup was held exclusively in Sydney, three cities - Brisbane, Perth and Sydney - are co-hosting the United Cup in 2023.
The event is taking place over 11 days, beginning on Thursday, December 29, 2022 and wrapping up on Sunday, January 8, 2023.
Each city is hosting two separate groups made up of three countries between December 29 to January 4, before the top four nations compete in Sydney from January 6 to 8.
Those top four nations will be those who win in their respective city, as well as the next-best performing team.
The full tournament schedule can be accessed here.
How are countries selected for the United Cup?
18 countries will feature in the inaugural tournament in 2023, with 12 countries selected from the nations of the top six men's and women's players, according to ATP and WTA rankings.
The other six teams qualify based on combined men's/women's rankings.
Which countries and players have been selected for the United Cup?
All 18 nations have been confirmed for the 2023 United Cup.
The locations, groups and players are outlined below.
Perth
Group A
Greece
| Stefanos Tsitsipas | Maria Sakkari |
| Michail Pervolarakis | Despina Papamichail |
| Stefanos Sakellardidis | Valentini Grammatikopoulou |
| Petros Tsitsipas | Sapfo Sakellaridi |
Belgium
| David Goffin | Elise Mertens |
| Zizou Bergs | Alison Van Uytvanck |
| Kimmer Coppejans | Magali Kempen |
| Michael Geerts | Kirsten Flipkens |
Bulgaria
| Grigor Dimitrov | Viktoriya Tomova |
| Dimitar Kuzmanov | Isabella Shinikova |
| Adrian Andreev | Gergana Topalova |
| Alexandar Lazarov | - |
Group F
France
| Arthur Rinderknech | Caroline Garcia |
| Adrian Mannarino | Alize Cornet |
| Manuel Guinard | Leolia Jeanjean |
| Edouard Roger-Vasselin | Jessika Ponchet |
Croatia
| Borna Coric | Petra Martic |
| Borna Gojo | Donna Vekic |
| Matija Pecotic | Tara Wurth |
| - | Petra Marcinko |
Argentina
| Diego Schwartzman | Nadia Podoroska |
| Francisco Cerundolo | Maria Carle |
| Federico Coria | Paula Ormaechea |
| Andres Molteni | - |
Brisbane
Group B
Poland
| Hubert Hurkacz | Iga Swiatek |
| Kamil Majchrzak | Magda Linette |
| Daniel Michalski | Weronika Falkowska |
| Lukasz Kubot | Alicja Rosolska |
Switzerland
| Stan Wawrinka | Belinda Bencic |
| Marc-Andrea Huesler | Jil Teichmann |
| Dominic Stricker | Ylena In-Albon |
| Alexander Ritschard | Joanne Zuger |
Kazakhstan
| Alexander Bublik | Yulia Putintseva |
| Timofey Skatov | Zhibek Kulambayeva |
| Denis Yevseyev | Gozal Ainitdinova |
| Grigoriy Lomaki | - |
Group E
Italy
| Matteo Berrettini | Martina Trevisan |
| Lorenzo Musetti | Lucia Bronzetti |
| Andrea Vavassori | Camila Rosatello |
| Marco Bortolotti | Nuria Brancaccio |
Brazil
| Thiago Monteiro | Beatriz Haddad Maia |
| Felipe Meligeni Alves | Laura Pigossi |
| Matheus Pucinelli de Almeida | Carolina Alves |
| Rafael Matos | Luisa Stefani |
Norway
| Casper Ruud | Ulrikke Eikeri |
| Viktor Durasovic | Malene Helgo |
| Andreja Petrovic | Lilly Haseth |
| - | - |
Sydney
Group C
USA
| Taylor Fritz | Jessica Pegula |
| Frances Tiafoe | Madison Keys |
| Denis Kudla | Alycia Parks |
| Hunter Reese | Desirae Krawczyk |
Germany
| Alexander Zverev | Laura Siegemund |
| Oscar Otte | Jule Niemeier |
| Daniel Altmaier | Anna-Lena Friedsam |
| Fabian Fallert | Julia Lohoff |
Czech Republic
| Jiri Lehecka | Petra Kvitova |
| Tomas Machac | Marie Bouzkova |
| Dalibor Svrcina | Jesika Maleckova |
| - | - |
Group D
Spain
| Rafael Nadal | Paula Badosa |
| Pablo Carreno Busta | Nuria Parrizas Diaz |
| Albert Ramos-Vinolas | Jessica Bouzas Maneiro |
| David Vega Hernandez | - |
Australia
| Ajla Tomljanovic | |
| Alex de Minaur | Zoe Hives |
| Jason Kubler | Maddison Inglis |
| John Peers | Sam Stosur |
Great Britain
| Cameron Norrie | Harriet Dart |
| Dan Evans | Katie Swan |
| Jan Choinski | Anna Brogan |
| Jonny O’Mara | Ella McDonald |
How to watch the United Cup
As the rights holders of the 2023 Summer of Tennis - including the Australian Open - Nine are broadcasting the United Cup in Australia.
Every match is available on 9Now and via their paid streaming service, Stan Sport.
Selected matches are being televised on Channel 9's primary channel throughout the tournament.
For international viewers, please check your local guides for broadcast details.
What happened to the ATP Cup?
Replacing the Hopman Cup in 2020, the ATP Cup has lasted just three years.
A men's-only tournament, it pitted nations together in a team competition format.
Team Serbia claimed the inaugural edition, with Team Russia (2021) and Team Canada (2022) the other victors.
Ultimately, the ATP Cup has been replaced due to the increasing co-operation between the men's and women's tennis tours (the ATP and WTA).
The $15 million prize pool for the United Cup reflects the backing mixed tournaments are receiving, as tennis prioritises efforts towards equality.
When is the 2023 Australian Open?
Next year's Australian Open will run from Monday, January 16 until Sunday, January 29.