Act of Consecration to Our Lady of the Miraculous Medal

O Virgin Mother of God,
Mary Immaculate,
we dedicate and consecrate ourselves to you
under the title of Our Lady of the Miraculous Medal.
May this Medal be for each one of us
a sure sign of your affection for us
and a constant reminder of our duties towards you.
Ever while wearing it,
may we be blessed by your loving protection
and preserved in the grace of your Son.
O most powerful Virgin,
Mother of our Saviour,
keep us close to you every moment of our lives.
Obtain for us,
your children,
the grace of a happy death;
so that, in union with you,
we may enjoy the bliss of heaven forever.

Amen.

O Mary, conceived without sin,
pray for us who have recourse to you.

O Mary, conceived without sin,
pray for us who have recourse to you.

O Mary, conceived without sin,
pray for us who have recourse to you. 

About the History of the Miraculous Medal 

Source: Wikipedia 

The Miraculous Medal (French: Médailleō miraculeuse), also known as the Medal of Our Lady of Graces, is a devotional medal, the design of which was originated by Saint Catherine Labouré following her apparitions of the Blessed Virgin Mary[2] in Rue du Bac, Paris, France. It was made by goldsmith Adrien Vachette.[3]

Our Lady of the Miraculous Medal
The Miraculous Medal design was executed by Adrien Vachette based on Saint Catherine Labouré's visions.
Location	Paris, France
Date	18 July 1830 27 November 1830
Witness	Saint Catherine Labouré
Type	Marian apparition
Approval	1836[1] Archbishop Hyacinthe-Louis de Quélen Archdiocese of Paris
Shrine	Chapel of Our Lady of the Miraculous Medal, Paris, France
Patronage	Special graces, architects, miners, prisoners

The Chapel of Our Lady of the Miraculous Medal in Paris

According to the teaching of the Catholic Church, the use of sacramentals such as this medal[4] prepares people to receive grace and disposes them to cooperate with it. 

More information on the Miraculous Medal, click here