Wales vs Scotland and France vs Ireland
2018 Six Nations will be 'most competitive ever' says Sam Warburton
Six Nations 2018: Can England make it three in a row?
Follow the 2018 Six Nations live on the BBC
Dates: 3 February-17 March
Coverage: Watch live on BBC TV, Red Button, Connected TVs, BBC Sport website and mobile app. Listen on BBC Radio 5 live, 5 live sports extra, BBC Sport website and app. Live text coverage on BBC Sport website and app.
The 2018 Six Nations Championship will be "the most competitive year ever", injured British and Irish Lions captain Sam Warburton has predicted.
Back-to-back title winners England are aiming to become the first nation in 135 years to win the title outright for three consecutive years.
But Warburton, who will be a BBC One pundit, believes no nation will remain unbeaten in this year's tournament.
"We won't see anybody winning the Grand Slam this season," he told BBC 5 live.
"This is the most competitive year since the tournament became the Six Nations. There are definitely four teams, and potentially France, who can all beat each other. It's wide open."
Wales face Scotland in the opening match of the 2018 Six Nations in Cardiff on Saturday, before Ireland travel to Paris to play France.
England get their campaign under way against last season's bottom side Italy in Rome on Sunday.
England aiming to make history
Six Nations 2018: Italy v England
Date: Sunday 4 February
Venue: Stadio Olimpico, Rome
Kick-off: 15:00 GMT
Coverage: Watch highlights on BBC Two, online and BBC Sport app from 18:00 GMT; listen on BBC Radio 5 live; text commentary on BBC Sport website.
England were denied a second consecutive Grand Slam in 2017 after defeat by Ireland in Dublin
Since the competition began as the Home Nations in 1883, there have been 20 back-to-back title wins, including England's latest double. In all previous 19 times, no-one has gone on to win three in a row.
Warburton won back-to-back titles with Wales in 2012 and 2013, but his side could only finish in third place the following year.
And the Welsh back-row says he "underestimated" how hard the task would be.
"Three in a row has never happened. There's a lot of pressure on England. I think I underestimated back in 2012 and 2013 how hard it is to win a Six Nations," he told BBC 5 live's rugby union show.
"England against Ireland on the final weekend at Twickenham, I would bet that would be a Championship game. And you'd probably have to go with home advantage.
"But if there's an upset in the first two weeks, suddenly the tournament is wide open for Scotland and Wales or Ireland. It's so so difficult to call."
Survival of the fittest
2018 Six Nations: Wales v Scotland
Venue: Principality Stadium
Date: Saturday, 3 February
Kick-off: 14:15 GMT
Coverage: Watch live on BBC One, Connected TVs, online and BBC Sport app from 13:15 GMT; listen on BBC Radio 5 live; text commentary on BBC Sport website.
The build-up to the 2018 Six Nations has been dominated by injuries, amid a backdrop of discussions around the length of the domestic playing calendar.
But the first match of this year's tournament is arguably the worst hit - Wales will be without six of their first choice players when they face Scotland in Cardiff.
Warburton, Jonathan Davies and Rhys Webb will miss the whole tournament. Three more British and Irish Lions - Taulupe Faletau, Liam Williams and Dan Biggar - will take no part in the opening round at least.
Rhys Priestland, Jake Ball and Dan Lydiate are also out, while wings George North and Hallam Amos were not considered match-fit for the first game.
"That Wales injury list is horrific," former Ireland centre Shane Horgan told BBC 5 live's rugby union show. "It's their best players and their most important players.
"It's almost impossible to see beyond that. These are some of the best players Wales have had in a generation and they're missing."
But while Wales' back-line has been decimated, Scotland are facing a crisis of their own in the pack.
Gregor Townsend's side have lost hookers Ross Ford and Fraser Brown, tight-heads Zander Fagerson and WP Nel, and loose-head trio Darryl Marfo, Allan Dell and Al Dickinson.
Scotland have not won in Cardiff for 16 years, but they captivated the rugby world with their high-energy displays in the autumn internationals.
They won two out of three Tests in November, including a victory over Australia, and were narrowly beaten by World Champions New Zealand.
And with England aiming for three consecutive titles, Scotland's fit again full-back Stuart Hogg could take home a triple of his own - a third player of the tournament award in succession.
Ireland favourites for the title?
2018 Six Nations: France v Ireland
Venue: Stade de France, Paris
Date: 3 February
Kick-off: 16:45 GMT
Coverage: Watch live on BBC One, Connected TVs, online and BBC Sport app from 16:15 GMT; listen on BBC Radio 5 live; text commentary on BBC Sport website.
Ireland are the only side to have beaten England under Eddie Jones, having thwarted their Grand Slam attempt during last year's Six Nations.
Joe Schmidt's side begin their assault on the title against an unpredictable French side, who have named teenage debutant Matthieu Jalibert at fly-half.
Horgan, who won 65 caps for his country, believes the current Ireland side are the favourites for the 2018 title.
"They're on the way to being the best team that Ireland have have ever had, certainly the most balanced team," he told BBC 5 live's rugby union show.
"In the front row in particular, Ireland now have four top quality props. They've never had that sort of depth. I'm convinced Tadhg Furlong is the most complete prop in the world at the moment."
2018 Six Nations will be 'most competitive ever' says Sam Warburton - BBC Sport