Drop-down lists are useful when you want to force the user to enter only specific values into a cell in an Excel sheet. The user is presented with a drop-down list and he has to choose any one value from it. If the user enters a different value, it will be rejected. For example, you may create a drop-down list where users select a day of the week or Yes/No. This little tutorial will show you how to add such a drop-down list to an Excel cell.