The Book of Common Prayer, originally compiled by the martyred Archbishop Thomas Cranmer, was the cornerstone of Reformation Christianity in England, and still serves as such for Anglican Christians across the globe. Cranmer brought together the various liturgies (worship services) used in England and on the continent, and produced a single version, informed by the principles of the Reformation, in English. The primary purpose was to provide a worshipful framework for the public reading of Scripture in the churches: like a long Bible reading plan with prayers attached.
The services most used in the Book of Common Prayer are Morning and Evening Prayer, Holy Eucharist (the Lord's Supper, or Communion), and Compline (prayer before retiring). All of the services in the BCP are designed for public use by congregations and small groups, but Morning and Evening Prayer and Compline are used very often for personal devotions.
The most common versions in the US are the 1979 and 1928 revisions, and the 1662 from England.
What I Like. The Offices in the Book of Common Prayer are Scripture-heavy: really geared toward a broad reading of Scripture, so that most of the Bible is read in a two year cycle. The content is also traditional in the historical sense, but with a Reformation tempering; prayers are offered that Christians have been offering for hundreds of years, with the Psalms (the prayers that Jesus prayed!) at the center, making place for intercessory prayer.
What I Didn't Like. Because the BCP is meant to be used in all seasons for all the services of the Church, there is a learning curve for its use, and holding both the Bible and the Prayer Book during devotional times can feel a little unwieldy at times. The volume isn't nearly as confusing as it looks, and it's invaluable as a devotional tool.
The Bottom Line. The Book of Common Prayer is a classic of the Western Christian tradition, and Christians of all denominations (and none) draw from its resources, and with good reason. This is the meat and potatoes of prayer books, both ubiquitous and affordable.