How many normalization forms exists

[maq.khan]

How many are the levels / forms of normalizaion exists?

also how much normalization should be done?

[krishnaindia2007]

The process of normalization breaks the data into smaller tables to reduce redundancy and make retrieving and managing that data more efficient. There are mainly 5 Normalization rules. In most of the cases we use first three normalization rules only.

1 Normal Form : A table is said to be in 1st Normal Form when the attributes are atomic
2 Normal Form : A table is said to be in 2nd Normal Form when all the candidate keys are dependant on the primary key
3rd Normal Form : A table is said to be third Normal form when it is not dependant transitively (when one non-key attribute is functionally dependent on another non-key attribute)

[debasisdas]

actually there are 7 but only 3 are used