So far, we have considered functions of one variable and developed differential calculus for functions of one variable, which enabled a deeper understanding of the relationship between the dependent and independent variables, as well as how a change in one variable affects another. However, in economic problems, the value of one variable usually does not depend only on the value of one other variable, but on several of them. Thus, for example, the demand for a product depends not only on the price of that product, but also on the prices of some other products, as well as income. The total cost of production depends not only on the level of production, but also on the price of inputs, etc. Thus, in this chapter we introduce the notion of a function of several variables and present some basic terms related to it. We present some basic real functions of n real variables, like linear function, monomials, and polynomials, and conclude by expanding the concept of a continuous function to functions of n real variables.