The human tissue Kallikrein gene family encodes 15 serine proteases. All Kallikreins share structural similarities including cysteine residues, a catalytic triad of His, Asp, and Ser residues, typically five coding exons, and varied intron phases. Kallikreins are predominantly secreted as inactive zymogens prior to activation by cleavage of an N terminal peptide, and all function extracellularly. Kallikreins can be activated autocatalytically, via other Kallikreins, or additional proteases. While structurally similar, Kallikrein family members have distinct functions and have key roles in many physiological and pathological processes. Many human tissue Kallikreins also show promise as cancer biomarkers, which may facilitate earlier detection and characterization of many forms of cancer. Kallikrein 15 is one of the fifteen kallikrein subfamily members whose gene is located in a cluster on chromosome 19. Increased levels are found in prostate cancer, which indicates its possible use as a diagnostic or prognostic marker for prostate cancer. Four splice variants, each encoding a distinct isoform, have been described.