Invalid and inconsistent data is one of most common problems in Spreadsheets. If the data supplied is not in the right format or is not entered consistently then any following formula's or calculations will either not work or worse still provide a result that is not correct. Excel provides a built-in Data Validation feature that can be included to any spreadsheet. Data Validation provides error checking and instructions for the user as they enter data to a spreadsheet. In this post we will demonstrate some simple examples of Data Validation on a customer address list.