Phosphatidylinositol-specific phospholipase C (PLC) is a family of enzymes that occupy a pivotal role in one of the largest classes of cellular signaling pathways known. Mammalian PLC enzymes have been divided into four major classes and a variety of subclasses based on their structural characteristics and immunological differences. There have been five invertebrate PLC-encoding genes cloned thus far and these fall within three of the four major classes used in categorizing mammalian PLC. Four of these invertebrate genes have been cloned from Drosophila melanogaster and one is from Artemia, a brine shrimp. Structural characteristics of the invertebrate enzymes include the presence of highly conserved Box X and Box Y domains found in major types of mammalian PLC as well as novel features. Two of the invertebrate PLC genes encode multiple splice-variant subtypes which is a newly emerging level of diversity observed in mammalian enzymes. Studies of the invertebrate PLCs have contributed to the identification of the physiological functions of individual isozymes. These identified roles include cellular processes such as phototransduction, olfaction, cell growth and differentiation.