Alu elements are the most abundant repetitive elements in the human genome; they emerged 65 million years ago from a 5' to 3' fusion of the 7SL RNA gene and amplified throughout the human genome by retrotransposition to reach the present number of more than one million copies. Over the last years, several lines of evidence demonstrated that these elements modulate gene expression at the post-transcriptional level in at least three independent manners. They have been shown to be involved in alternative splicing, RNA editing and translation regulation. These findings highlight how the genome adapted to these repetitive elements by assigning them important functions in regulation of gene expression. Alu elements should therefore be considered as a large reservoir of potential regulatory functions that have been actively participating in primate evolution.