1.Roll-Up Summary field can be created only in a OBJECT which is referred as a object with a master detailed relationship field.
2.Roll-Up Summary field can only created for Master-detail Relationship.
3.Roll-Up Summary field can not be created for Look-up Relationship.
4.It Derives the data from child Object.
5.We can’t change field type of a field that we reference in a roll-up summary field.
6.Auto numbers are not available here.
7.Roll-Up Summary FIELDS are not available for mapping lead fields of CONVERTED fields.

1.Roll-Up Summary field can be created only in a object which is referred as a object with a master detailed relationship field.
2.Roll-Up Summary field can only created for Master-detail Relationship.
3.Roll-Up Summary field can not be created for Look-up Relationship.
4.It Derives the data from child Object.
5.We can’t change field type of a field that we reference in a roll-up summary field.
6.Auto numbers are not available here.
7.Roll-Up Summary fields are not available for mapping lead fields of converted fields.