The Bhagavad-Gita consists of 700 verses and 18 chapters. It was originally revealed in the classical language of Sanskrit by Lord Krishna  to Arjuna on the battlefield of Kuruksetra in 3102 B.C.; just prior to the commencement of the Mahabharata war. Bhagavad-Gita is the very essence of the Vedas which literally translates as the Song of God. It was written by Ved Vyaas.

Each chapter is called yoga. Yoga is the science of the individual consciousness attaining communion with the Ultimate Consciousness. So each chapter is a highly specialized yoga revealing the path of attaining realization of the Ultimate Truth.

The first six chapters have been classified as the Karma Yoga section as they mainly deal with the science of the individual consciousness attaining communion with the Ultimate Consciousness through actions. 

The middle six chapters have been designated as the Bhakti Yoga section as they principally are pertaining with the science of the individual consciousness attaining communion with the Ultimate Consciousness by the path of devotion.

The final six chapters are regarded as the Jnana Yoga section as they are primarily concerned with the science of the individual consciousness attaining communion with the Ultimate Consciousness through the intellect.