The Doctrine and Covenants (sometimes referred to as D&C) is a part of the open scriptural canon of Mormonism, together with the Bible and The Book of Mormon. In the Church of Jesus Christ of Latter-day Saints (LDS Church), these three books, together with The Pearl of Great Price are referred to as the "Standard Works".
The book is a later version of The Book of Commandments, which was published in 1833 (about 18 original copies exist today). This earlier book was a collection of 65 purported revelations given to Joseph Smith, Jr In 1835, these earlier revelations were combined with additional revelations, together with a series of doctrinal discourses used in the school of the prophets in Kirtland, Ohio entitled Lectures on Faith. The resulting combination was entitled The Doctrine and Covenants; the "doctrine" portion consisted of the Lectures on Faith, while the "covenants" portion consisted of Smith's revelations. This book was officially accepted as part of the Mormon canon on August 17, 1835.
Today, the book is published in a number of versions, depending on which church publishes the book. The Lectures on Faith portion of the book was removed by the Community of Christ (then known as the RLDS Church) in 1897, and by the LDS Church in 1921. In addition, both churches have added additional material, including additional purported revelations and other materials by Smith and other church leaders.
The book is organized in "sections", with each section representing an individual revelation. The LDS Church's edition also contains two "Official Declarations" at the book's conclusion, the first renouncing polygamy in 1890, and the second renouncing racial discrimination in ordaining members to the Priesthood in 1978. An "Official Declaration" is not a revelation, but an announcement that a revelation was recieved. In neither case is the entire revelation included in the Doctrine and Covenants.
The Doctrine and Covenants is often abreviated as "D&C" which many within Mormonism dislike because the abbreviation is also used for a medical procedure, dilation and curettage, related to abortion.