The Cecil Papers are a privately held archive of approximately 30,000 sixteenth and seventeenth-century manuscripts, consisting principally of the correspondence of William Cecil, Lord Burghley (1520-1598) and his son Robert, the 1st Earl of Salisbury (1563-1612). These two men dominated the administration of government during the reign of Elizabeth I and the first eight years under her successor, to the extent that critics suggested that England was becoming a regnum Cecilianum. Both Cecils held a variety of public appointments; they were both long-serving Secretaries of State who achieved even greater political power as Lord High Treasurer. The collection documents their various official roles. In addition, the collection contains documents acquired by Robert Cecil that had belonged to his rival, Robert Devereux, the 2nd Earl of Essex. The papers span the period 1520-1668, from the birth of William Cecil, Lord Burghley, to the death of William Cecil, 2nd Earl of Salisbury.^