West Brom recruit Reading forward Long
The 24-year-old, who has a further one-year option, is West Brom's sixth close-season signing and comes with an impressive scoring pedigree having netted 25 goals in 51 starts last term.
"Shane is one of the most talented young strikers outside the Premier League and I'm delighted to welcome him to the club," West Brom manager Roy Hodgson told the club's website which said the fee was undisclosed.
"The great thing about him [Long] is that even though he is still only 24 he has six years' worth of experience of Premier League, Championship and international football and has margin for improvement in his game."
Long, who made his Ireland debut in 2007 and scored six goals in 21 games for his country, has rejoined the national squad for Wednesday's friendly with Croatia in Dublin.
However, Long's international team-mate Seamus Coleman has been sidelined by a torn right ankle ligament sustained in Everton's friendly with Villarreal on Friday.
The 22-year-old will visit a specialist this week but the club said on its website that it was too early to put a time scale on his recovery.