The USCCB is the gathering of all the Catholic bishops of the United States from both the Latin (Western Rite) and Byzantine (Eastern Rite) Catholic churches. Each year the group meets twice to discuss topics and issues of concern for the Catholic Church in the nation.
Catholic bishops of the United States formed the National Catholic War Council (NCWC) in 1917 to enable Catholic Americans to contribute funds to provide spiritual care and recreation services to servicemen during World War I. In 1919, Pope Benedict XV urged the hierarchy (the world’s bishops) to join him in working for peace and justice, which resulted in the American bishops renaming the organization the National Catholic Welfare Council. Since 1966, after the close of Vatican II, it was known as the National Conference of Catholic Bishops (NCCB) with a sister branch called the United States Catholic Conference (USCC). The name was again changed in 2001 to its current title (USCCB) when the two merged into one entity.
Canon Law is very explicit on the authority of all national episcopal conferences. They are not parallel legislative bodies in the way that the Senate and House of Representatives are. They are not equal or superior to the Holy See which represents the pope and all the departments of the Curia which implement his papal authority of universal jurisdiction. Episcopal conferences are seen as exercises of subsidiarity, which is a principle endorsed by Vatican II that, when possible, work should be done at lower levels by those closer to the scene. Hence, each pastor of a church decides for himself the times of Mass, whereas the diocesan bishop makes regulations on how early Saturday evening Mass can take place and the national conference of bishops decide which holy days are obligatory (pending final approval of Rome).
Sometimes, it helps to see Rome and the Vatican as being like the White House (executive branch), Congress (legislative branch), and Supreme Court (judicial branch) all rolled into one federal authority, with the local diocesan bishop being like the individual states and the local pastor of the parish being like the municipal authority. In this analogy, the USCCB would be akin to a meeting of state governors.
As an assembly of the hierarchy of the United States and the U.S. Virgin Islands, the USCCB can at times exercise authority, but individual member bishops never lose their autonomy to govern their respective dioceses. The decree Apostolos Suos issued by Pope John Paul II in 1997 states that episcopal conferences do not possess per se doctrinal authority, which is binding and superior to each bishop who comprises them. If doctrinal declarations from a conference are approved unanimously by the bishops, they can be published in the name of the conference itself, and the faithful must adhere to them. Where unanimity is absent or on matters of a liturgical nature, subsequent Vatican approval is necessary.