The collection consists largely of seventeenth- and eighteenth-century correspondence. The chief correspondents are the members of the family most active in public life, and their letters are on the whole more concerned with public than with personal affairs, though there is some discussion of family matters in the seventeenth-century letters. The most important and extensive correspondence is that of the 1st Marquess of Tweeddale, which dates from 1660 to 1697, and covers most of his political career; and that of the 4th Marquess of Tweeddale, most of which dates from 1742 to 1746, his period of office as Secretary of State for Scotland. Lord Charles Hay's papers concern the campaigns of 1743-1745 against France, and the Seven Years' War in America; the 8th Marquess's papers concern (though very briefly) the Peninsular War.