Lookup filters on relationship fields
Key Takeaway
A lookup filter limits which records users can select in a relationship field. In Lightning Experience, all lookup filters are required. Deactivating a filter keeps its setup, but deleting it is permanent.
A lookup filter is an admin setting on a relationship field that limits which records users can pick for that field. It improves data quality by blocking invalid choices. It also saves users time, because the lookup dialog (the search dialog where users pick a record) shows only relevant records.
What a lookup filter does
A lookup filter works on lookup, master-detail, and hierarchical relationship fields. It restricts two things for the field: which values are valid, and which records appear in the lookup dialog.
For example, you can limit the Account Name field on opportunities to accounts with a Customer record type, or to active accounts only.
Lookup filters work in both Salesforce Classic and Lightning Experience, in all editions except Database.com. Salesforce enforces them when you load data through the API (version 16.0 and higher). They also appear in the partner portal and Customer Portal.
Lookup filters aren't available for external lookup relationship fields. They also aren't available for the standard Product field when you create an OrderItem.