Many protein-coding genes in eukaryotes have the capacity to produce circular RNAs (circRNAs). CircRNAs are stable and covalently closed products generated from backsplicing. Their biogenesis is regulated by multiple factors, with RNA-binding proteins (RBPs) playing a critical role. RBPs bind to flanking introns of the circularizing exons, bringing the intervening splice site into close proximity and thereby facilitating the process of backsplicing. In this chapter, we summarize the literature on RBP-mediated circularization in circRNA biogenesis, illustrating how RBPs influence RNA fate and gene regulation.