This chapter discusses the distinct peculiarities of the calcium homeostatic mechanisms in Toxoplasma gondii, as well as the methods used in their study. A variety of cellular functions are regulated by fluctuations of the cytosolic concentration of Ca2+. Ca2+ regulation in T. gondii differs in several aspects from the processes that occur in other eukaryotic cells, providing great opportunities for targeting them for new therapies. Acidocalcisomes are distinct calcium-storage organelles present in T. gondii, in which calcium is mostly bound to poly P, although no information is available on second messengers involved in Ca2+ release from these organelles. Stimulation of Ca2+ influx across the plasma membrane is one of the key events in transmembrane signaling. Ca2+ storage organelles capable of both high affinity uptake and rapid triggered release of Ca2+ are believed to be ubiquitous among eukaryotes.