This chapter explains why it is important to make robust user proof spreadsheets, and how to create spreadsheets that users cannot break. Readers are encouraged to think beyond their own needs for spreadsheets, and to consider the change in approach that is required when creating spreadsheets for wider distribution. There are a number of tools available to maximize data integrity, including data validation, hiding data, tables, and limiting what uses can do with cells. These tools are explained in simple step-by-step terms, using library specific examples. For the readers that are interested in stretching themselves, this chapter also explains the use value of dependent lookups, and explains in detail how these formulas work.