Srimad Bhagavad gita and Srimad Bhagavatam.

The Srimad Bhagavatam is generally mistaken to be the same as the Bhagavad-gita. The Bhagavad gita , which was spoken by Lord Krishna on the battlefield of Kurukshetra, is the most famous book in the entire universe because it is spoken by God Himself. One may go to any part of the world and one will find that everywhere the glories of the book are sung. Any serious seeker of the Absolute Truth will not be unaware of the exalted nature of the divine book.
Since the Bhagavad gita was spoken on the battlefield to induce Arjuna to fight, it is concise in nature and many higher transcendental exchanges of love are not discussed. These topics are discussed in detail in the Srimad Bhagavatam, which is considered the graduate study of the Bhagavad-gita. The Srimad Bhagavatam is one of the eighteen puranas, and is therefore, also known as the Bhagavata Purana. It is considered to be the essence of all the Vedas. The Vedas are compared to a desire tree because all kinds of knowledge that one may desire, are available in them. But Srimad Bhagavatam is the ripened fruit of that desire tree because it is giving the highest knowledge of the Supreme Personality of Godhead and the reciprocation of loving exchanges between Him and His devotees.