Lookup Relationship Explained
Lookup relationships create a foreign-key reference from one object (the child) to another (the parent). The child record stores the parent's record ID in a lookup field, and users can navigate between related records via the lookup field or related lists. Unlike master-detail relationships, lookup relationships are optional by default (the lookup field can be blank) and the child record has its own independent OWD and sharing settings.
Lookup relationships support self-relationships (an object referencing itself, such as an Account's Parent Account), hierarchical relationships (special self-lookup on the User object for the role hierarchy), and external lookups to external objects. They do not support roll-up summary fields natively (though Flow or Apex can replicate this). Admins can configure what happens when the parent is deleted: clear the lookup value, prevent deletion, or (in some cases) delete the child. Lookups are the right choice when the child record has an independent lifecycle. Clientell AI can recommend the optimal relationship type when you describe your data model requirements.