The full-back has agreed a two-year deal with the Light Blues following his release from Bristol City and will be registered on September 1 when the club's transfer embargo is lifted.
Foster spent the 2010-11 campaign on loan at Ibrox while at Aberdeen and played his part in winning the league in Walter Smith's final season at the helm. And, despite vastly different circumstances this time around, he is relishing this challenge just as much.
Foster said: "As a footballer you want to win games and trophies and medals. You can only win the division you're in so to win the Second Division would be as big an achievement as winning the SPL."
Foster, who was reminding fans that the deadline for season ticket renewals is this Friday, added: "If anything, my time away has just reassured me of how big Rangers are. You leave Scottish football and you meet Rangers fans in England and wherever you go and you hear they're getting 50,000 people at home games in the Third Division.
"Everything from Murray Park to the stadium just screams out that they're a massive club. A club as big as Rangers should be in the SPL and one of the reasons I want to come back is to get them to where they should be."
Foster's best displays during his first spell at Rangers were arguably those on the European stage, whereas next season he will play against the likes of Stranraer and Brechin.
He said: "It was one of the things I had to consider but it's a new challenge, it's different. At the end of the day it's a game of football you want to win to ultimately win the league. You just need to adapt to these things and do your best."
Foster says he had always hoped for a return to Rangers after an enjoyable loan spell and was pleased to be able to negotiate his departure from the relegated Robins.
He said: "It was something I thought about when I was here. The fans were great with me, I played in some great games, the stadium is amazing. It's something I always wanted to do and I'm glad now I've been given the opportunity."