Create a Lookup Field from Object Manager when you want to relate a record on one object to a record on another, without the tight coupling of a master-detail relationship. The flow below covers the standard path for a custom or standard object.
- Open the object in Object Manager
In Setup, go to Object Manager and select the child object, the one that will store the link. Click Fields and Relationships, then New.
- Choose the Lookup Relationship type
On the data type screen, select Lookup Relationship and click Next. Then pick the related object, the parent that records will point to, and continue.
- Label and configure the field
Enter the Field Label and let the name auto-fill. Optionally make the field required, and add a Lookup Filter if you want to restrict which parent records users can pick.
- Set the delete behavior
For an optional lookup, choose what happens when the parent is deleted: clear the field, block the deletion, or cascade delete the child where that option is offered.
- Add to layouts and save
Set field-level security, add the field to the page layouts that need it, choose which related lists show the child records, then save.
The user-facing name of the lookup field shown on layouts and in the picker.
The object whose records this lookup points to; chosen on the data type step and not changeable after creation.
The internal name used in code and integrations; auto-derived from the label but editable before saving.
- Roll-up summary fields do not work on plain lookups; you need a master-detail relationship, or a flow or Apex, to summarize child records onto the parent.
- Each custom object allows up to 40 relationship fields total, counting master-detail and lookup together, so plan the schema before you hit the cap.
- Cascade delete (Delete this record also) bypasses sharing and security, is disabled by default, and is often only available after Salesforce enables it.
- Converting a lookup to master-detail later requires that every existing child record already has a value in the lookup field.