Use drop-down lists to ensure that the value in a cell matches one of a set of pre-defined values, for example a list of departments. Drop-down lists are part of Excel’s Data Validation feature, a process of applying rules that restrict what users can enter on a worksheet.
This short video explains how to create a drop-down list in a cell using the Data Validation command. The video uses Excel 2011 for Mac, however, the feature works in an almost identical way in Excel for Windows.