mine               El mío, la mía, los míos, las mías
yours              El tuyo, la tuya, los tuyos, las tuyas
his, hers, theirs, El suyo, la suya, los suyos, las suyas
yours, (polite)     
ours               El nuestro, la nuestra, los nuestros, las nuestras
yours (familiar)   El vuestro, la vuestra, los vuestros, las vuestras

The Possessive Pronoun must be preceded by the definite article except when it follows the verb "to be" ("Ser") and ownership is asserted.

Examples:

Su casa es más importante que la mía
His firm is more important than mine.

Usted ha acabado su trabajo, pero yo no he principiado el mío
You have finished your work, but I have not started mine.

Estos títulos y acciones son míos.
These bonds and shares are mine (viz., belong to me).[2]

Possessive Adjectives Emphatic.

If any emphasis is placed on the possessive adjectives, the forms of the possessive pronouns are used, following the noun, as:

Quiero la maleta mía y no la de su amigo
I want my portmanteau, not your friend's.

"A friend of mine," "a customer of yours" will be translated "un amigo de los míos," "un cliente de los suyos," or also "un amigo mío," "un cliente suyo," without the preposition "de."

The Possessive Pronoun preceded by the neuter article lo denotes "property in general," as:

Lo mío               mine--that which is mine
Lo nuestro           ours--that which belongs to us
Lo suyo/lo propio    one's own property
Lo ajeno             other people's property

In addressing a person translate "my," etc., by "mío," etc., as:

Amigo mío: My friend.
Muy Señor mío (usual introduction to a Spanish letter).

But if the noun is qualified by an adjective, both "mi" and "mío" are
used ("mi" is more general), as Mi querido amigo (my dear friend).