Carrageenan, a kind of linear sulfated polysaccharides consisting of D-galactose with alternating alpha-1,3 and beta-1,4 linkages, has been widely applied in the food and cosmetic industries as thickening and gelling agents due to excellent properties, such as gel-forming ability and chemical stability. It can be degraded by carrageenases to produce a series of even-numbered carrageenan oligosaccharides, which exhibit various fascinating functions, such as anti-inflammation, anti-coagulation, anti-tumor, and anti-thrombosis effects. Numerous carrageenases have been isolated and identified from various sources. The enzymes are grouped into three categories, namely kappa-carrageenase, iota-carrageenase, and lambda-carrageenase based on their substrate specificities and primary sequences, respectively. Elucidating the paradigm of the enzyme at every aspect would definitely enhance our understanding of the marine carbon cycling and natural evolution of glycoside hydrolases (GHs). The structural features of these enzymes have been fully illustrated, which will improve our knowledge of its catalytic mechanisms. In this review, we have summarized the recent progresses of major sources, category, and the enzyme's biochemical characteristics. Additionally, structural characteristics and catalytic mechanisms have been introduced in detail. We conclude with a brief discussion of the potential of the carrageenases in possible future applications in preparing functional oligosaccharides with versatile activities. This comprehensive information should be helpful regarding the application of carrageenases.