Striker Lukaku joins West Brom on loan
The 19-year-old teams up with former Chelsea assistant coach Steve Clarke, who is starting his first season as a manager.
Lukaku made just 12 appearances last season after joining Chelsea in August from Anderlecht and made his first league start on the last day of the season against Blackburn Rovers.
"After last season, where I was able to adjust and prepare for this season, I can't wait to start at West Brom," Lukaku told Chelsea TV.
"It will also be a good learning school for me where I need to work hard with the players around me."
Lukaku began his professional career with Anderlecht and was topscorer in the Belgian league in the 2009/10 season at the age of sixteen.