This chapter is designed for the least squares method . It begins with the least squares method to determine a polynomial of degree n well fitted to m discrete points (xi, yi), i = 1, 2, ...,m, when n ≤ m. In the simplest form, the line of regression through m points is determined. The algorithm to find well fitted function to given discrete data is also presented. The Mathematica modules are designed and example illustrating the method are provided . The chapter ends with a set of questions.
Keywords: The least squares method, Regressions.