The 32-year-old joins after a disappointing campaign with Hamburg and has signed a three-year deal with the newly promoted side
The 32-year-old left Hamburg following a disappointing season in the Bundesliga and now begins his second spell in La Liga after a two-year stint with Real Madrid.
After his second spell at HSV ended, Van der Vaart rejected the chance to rejoin Ajax in order to sign for Betis, who will play in La Liga next term after winning promotion last season.
"I'm very happy to come here. It's a great club and I really can't wait to start," said the Dutchman. "For me it is a dream because my family lives in Chiclana, which is very close, and I like playing in Spanish football.
"I always give 100 per cent when I play. I want to win and score goals, besides giving assists. This stadium is always full and that's why I really want to win many games.
"I have a lot of experience. I have to play well. We have to enjoy it because football is the best job in the world.