The History of Yoga is complex and detailed

4) Serving the lotus feet of the Lord - providing a form of physical service.

5) Worshiping the Lord - deity worship (arcana) is a popular form of this within India.

6) Offering prayers to the Lord - any form of prayer offered to please God.

7) Serving the Lord - offering a service for Lord's pleasure, such as preaching activity.

8) Building a friendship with the Lord - having an internal, loving relationship with God.

9) Surrendering everything unto the Lord - surrendering one's thoughts, actions and deeds to God.

These nine principles of devotional service are described as helping the devotee remain constantly in touch with God.

The processes of japa and internal meditation on the aspirant devotees's chosen deity form (ishta deva) are especially popular in most bhakti schools.

Bhakti is described as a yoga path, in that it's aim is a form of divine, loving union with the Supreme Lord. The exact form of the Lord, or type of union varies between the different schools, but the essence of each process is very similar.

The Bhagavad Gita

While it has an extensive list of philosophical and religious associations, the Bhagavad Gita is also seen as a cornerstone for Hindu Bhakti theism, especially within Vaishnavism. However, it has been interpreted by many as being a manual not limited just for devotees of Krishna. Whatever be the case, it is adamant, in Krishna's words, that love and innocent, pure intention is the most powerful motive force in a devotee's spiritual life. It is a very succinct and comprehensive statement on the mindset of the Bhakta (loving devotee), regardless of the form of God chosen:

man-mana bhava mad-bhakto, mad-yaji mam namaskuru, mam evaishyasi yuktvaivam, atmanam mat-parayanah

"Engage your mind always in thinking of Me, become My devotee, offer obeisances to Me and worship Me. Being completely absorbed in Me, surely you will come to Me." (B-Gita 9.34)

bhaktya mam abhijanati, yavan yas casmi tattvatah, tato mam tattvato jnatva, visate tad-anantaram

"One can understand Me as I am, as the Supreme Personality of Godhead, only by devotional service. And when one is in full consciousness of Me by such devotion, he can enter into the kingdom of God." (B-Gita 18.55)

The Branches of Bhakti

The various bhakti movements are monotheistic in their aim, being primarily devoted to worship of either Vishnu or Shiva as the Supreme God or His personal energy, known as Shakti.

These movements, which followed the establishment of the three Vedanta systems, rejuvenated Hinduism through their intense expression of faith and responsiveness to the emotional and philosophical needs of India, illustrated by Bharatanatyam, and can rightly be said to have affected the greatest wave of change in Hindu prayer and ritual since the advent of Adi Shankaracharya. There have been bhakti movements right through Indian history.

The philosophical schools changed the way people thought, but Bhakti was immediately accessible to all, calling to the instinct emotion of love and redirecting it to the highest pursuit of God and self-realization. In general a liberal movement, its denouncement of caste offered recourse for Hindus from the orthodox Brahaminical systems. Of course, however, Bhakti's message of tolerance and love was not often heeded by those ensconsed in the societal construct of caste.

Altogether, bhakti resulted in a mass of devotional literature, music, dance and art that has enriched the world and gave India renewed spiritual impetus, one eschewing unnecessary ritual and artificial social boundaries."1

1.  Excerpt taken from wikipedia http://en.wikipedia.org/wiki/Bhakti_yoga