SharePoint Cascaded Lookup is a powerful look-up tool that greatly enhances the lookup functionality already native to SharePoint. It quickly cross-references existing data from a list or site within the same site collection and then applies a combination of filters to reduce the number of options presented in the dropdown menu of your lookup field. To use it, you set a combination of filters available in both the source list (the list you are looking up from) and the target list (the list where you want to add looked-up information) to ensure that only applicable values are displayed as choices in the dropdown list.