Krsna (pronounced "Krishna"),The Supreme Personality of Godhead, is a summary study of the tenth canto of the Srimad-Bhagavatam. The Bhagavatam is an encyclopedic, 18,000 verse text—divided into twelve Cantos—chronicling many of Krishna's various incarnations over the millennia. It also describes the creation and cosmography of the material universes, and the lives of many pure devotees of Krishna and how they attained perfection.
The tenth canto of the Bhagavatam focuses on Krishna Himself and His activities when He appeared on earth five thousand years ago. In Krishna, The Supreme Personality of Godhead—popularly known as "Krishna Book"—we see the private life of the Supreme Person. Behind all the omnipotence and majesty, Krishna is the all-attractive, fun-loving, perfect person, eternally reciprocating unlimited varieties of loving relationships with His devotees.
His Divine Grace A.C. Bhaktivedanta Swami Prabhupada wrote "Krishna Book" before he had even fully completed his translation and commentary on the Bhagavatam. He wanted people to hear about Krishna the person and His activities, in English, from an authorized representative of the Krishna-bhakti tradition. As he mentions in his Introduction, this was so they wouldn't risk mistaking Krishna to be just another human being and his pastimes as mundane adventure/romance stories.
It should be said, however, that fans of adventure and romance will find nothing lacking in this contemporary recounting of Krishna's activities.