While some players such as Maro Itoje, Alun Wyn Jones, Stuart Hogg and Tadhg Furlong are expected to be included in the touring party, generally there is serious competition for places across the squad.
However, as is always the case, form will also play a crucial part in the selection process, with established players coming under pressure from those who might not generally be seen as contenders.
Here are five such players, whose form in this season’s Six Nations has seen them move into contention for a place in the Lions squad.
Openside flanker is so competitive for the summer - Sam Underhill, Justin Tipuric, Peter O'Mahony, Josh van der Flier and Tom Curry all in the running - but based on opening three rounds then Watson is the man.
DID YOU KNOW? At the start of his English professional career he moved to Oakham in Rutland and was at the Leicester Tigers Academy
What a time to find the form of your life. As well as executing all the basics to a high standard, the dynamic loosehead also brings exceptional handling skills to the party. He thrives in the pivot role, is good around the park and is strong in the tight. Right now, he’s in pole position to take the jersey for the Lions.
3. Ronan Kelleher (Ireland)
Position: Hooker Age: 23 Club: Leinster Caps: 9
The Leinster hooker has been highly spoken of as a coming talent for a few seasons now, and at 23 with nine caps under his belt, his club form looks to have assured his place as the permanent Ireland hooker. With Ken Owens form inconsistent, there is a real opportunity for him to get into the Lions squad.
DID YOU KNOW? Kelleher was initially an outside-back and then a back-row for much of his underage years
Although the powerhouse was one of the stars of the last two Lions tour, the big winger has failed to recapture that form in recent seasons. Nevertheless, since moving into the centre North has been playing some of his best rugby. He covered as if his life depended on it against England and ran hard with ball in hand in round one, beating five Irish defenders.
DID YOU KNOW? North is the second highest all time try scorer for Wales behind Shane Williams.
5. Louis Rees-Zammit (Wales)
Position: Wing Age: 20 Club: Gloucester Caps: 7
As Bryan Habana, Jonny May, Makazole Mapimpi and others have shown, there is no substitute for pace. And Rees-Zammit has it by the bucketload, scoring three tries in the opening three rounds. He's also been adding to his game, showing some deft handling and increasingly astute defensive awareness to merge with his obvious attacking instincts. A proper Lions bolter