Assuming little familiarity with basic iterative methods and no acquaintance with multigrid, this tutorial begins from first principles. First, conventional relaxation methods applied to systems of linear equations are analyzed, since an understanding of their convergence properties and limitations is essential to multigrid. Second, the fundamental two-grid cycling scheme is discussed, leading to the introduction of the necessary intergrid transfer functions. The standard multigrid schemes are then presented. This tutorial concludes with an explanation of "why multigrid works." Adopted for classroom use by the University of Colorado, California Institute of Technology, Kansas State University, and North Carolina State University (partial listing).