The term ‘Probiotics’ is used to describe live microorganisms, which, when administered in adequate quantities, confer health benefits. The term probiotics was first introduced in 1965 by Lilly and Stillwell, who defined it to be microorganisms acting as growth promoters for other microorganisms. These microorganisms may include Lactobacillus, Streptococcus, Bifidobacterium, Saccharomyces, Aspergillus, Enterococcus etc., as well as a mixture of other microorganisms. The chapter focuses on providing a comprehensive and up-to-date review of probiotics that have been isolated from fermented fish-based products.