Neuronal Ca2+ signals occur in a very complex way. Direct imaging of Ca2+ changes in the soma, dendrites, and even single spines on fast time-scales greatly helps us understand the generation mechanism of diverse Ca2+ signaling events. However, Ca2+ imaging itself does not give information about the causal relationships between specific Ca2+ signals and specific functions. With the rapid improvements of new caged compounds, application or usage of uncaging/caging techniques has been expanded widely in biological research. Using caged compounds, the Ca2+ concentration in the target area can be either increased or lowered on a given time scale to various degrees. The most important advantage of the uncaging/caging technique is to control the intensity, duration, and area of light with high precision at a single cell level, providing very accurate control of biomolecules within a limited space at a given time. This chapter discusses how to use caged Ca2+ compounds in studying neuronal functions and Ca2+ signaling.