This code supports the text in Ayse Imrohoroglu, Selahattin Imrohoroglu and Douglas H. Joines, Computing Models of Social Security, in Ramon Marimon and Andrew Scott (eds), Computational Methods for the Study of Dynamic Economies, Chapter 10, Oxford University Press. This chapter describes in detail the calculations of two recent papers with large scale overlapping generations general equilibrium models.The first part explains how to set up a large scale model and how to incorporate various forms of uncertainty in the model. (crucial for explaining some real-life economic phonomena). The second paper simulates the effects of a demographic transition on the American social security system. The program provided (in Fortran) are the ones of a recent paper of the three authors, "Social Security in an Overlapping Generations Economy with Land", which has been published in the Review of Economic Dynamics. The programs are a generalized version of the programs of the first part of the paper.