Creating a Lookup Relationship is one of the most-done admin tasks in any Salesforce org. The configuration is simple but the design decisions about cascade behavior and filtering matter for the life of the relationship.
- Open Setup and navigate to the child object
Setup > Object Manager > select the child object > Fields & Relationships > New.
- Pick Lookup Relationship as the field type
The wizard differentiates Lookup Relationship from Master-Detail Relationship up front; pick Lookup when the child can exist independently.
- Pick the related-to object
The dropdown lists every standard and custom object the lookup can target. Pick the parent.
- Set the Field Label, Field Name, and child relationship name
The Label is what users see; the Field Name is the API name; the Child Relationship Name is what reverse-traversal queries use (Account.Opportunities__r style).
- Configure required and unique flags
Decide whether the lookup is platform-required (cannot be null) and whether it must be unique (each parent can have only one child of this type). Most lookups are neither.
- Add Lookup Filter if needed
Restrict which parent records are pickable through a formula. Useful for "show only active Accounts" or "show only Contacts on the current Account."
- Configure cascade delete behavior
Decide what happens when the parent gets deleted. Clear the lookup (default), prevent the delete, or cascade-delete the child.
- Add the field to Page Layouts and configure FLS
A new field is invisible without Page Layout placement and FLS grants on the relevant Profiles or Permission Sets.
- Save and test
Confirm the lookup works in the UI and that any planned automation (triggers, Flows, formulas) reads the field correctly.
- Lookup Relationships default to optional. Make them required through the field definition or a validation rule when the data demands it.
- Default cascade behavior is to clear the child's lookup on parent delete. Pick the alternative behavior when data semantics require it.
- Lookup Filters narrow the picker but evaluate at runtime. Heavy filters can slow lookup-search performance noticeably.
- Lookup Relationships do not propagate sharing or ownership. If the child needs to inherit the parent's sharing, use Master-Detail instead.