Endolysosomes are emerging as key players that generate as well as respond to intracellular Ca(2+) signals. The role of Ca(2+) in modulating acidic organelle function has long been recognized, but it is now emerging that acidic organelles also act as intracellular Ca(2+) stores; they actively sequester Ca(2+) in their lumina and release it to the cytosol upon activation of endolysosomal Ca(2+) channels. This local Ca(2+) signal is crucial for endolysosomal function and/or global Ca(2+) signaling. Importantly, defects in endolysosomal Ca(2+) are associated with disease. This chapter discusses several complimentary approaches to monitor endolysosomal Ca(2+), with particular emphasis on the inherent pitfalls that can plague the unwary.