Yes, there are double and triple integrals—and even multiple integrals in equations (∫∫, ∫∫∫, and so on). For example, the integration of a function of three variables, w = f(x, y, z), over a three-dimensional region R in xyz-space (three-dimensional space) is called a triple integral. The notation is as follows:

To compute the iterated integral, we need to integrate with respect to z first, then y, then x. And when we integrate with respect to one variable, all the other variables are assumed to be constant.