Cereal brans and grain endosperm cell walls are key dietary sources of different types of arabinoxylan. Arabinoxylan is the main group of hemicellulosic polysaccharides that are present in the cell walls of monocot grass crops and hence in cereal grains. The arabinoxylan polysaccharides consist of a backbone of β-(1→4)-linked xylopyranosyl residues, which carry arabinofuranosyl moieties, hence the term arabinoxylan. Moreover, the xylopyranosyl residues can be acetylated or substituted by 4- O-methyl-d-glucuronic acid. The arabinofuranosyls may be esterified with a feruloyl group. Feruloylated arabinoxylo-oligosaccharides exert beneficial bioactivities via prebiotic, immunomodulatory, and/or antioxidant effects. New knowledge on microbial enzymes that catalyze specific structural modifications of arabinoxylans can help us understand how these complex fibers are converted in the gut and provide a foundation for the production of feruloylated arabinoxylo-oligosaccharides from brans or other cereal grain processing sidestreams as functional food ingredients. There is a gap between the structural knowledge, bioactivity data, and enzymology insight. Our goal with this review is to present an overview of the structures and bioactivities of feruloylated arabinoxylo-oligosaccharides and review the enzyme reactions that catalyze specific changes in differentially substituted arabinoxylans.