Love is one of the most popular topics of ballads. There are ballads about unrequited love (Barby Ellen), love overcome against all barriers (Tam Lin), the accidental killing of a loved one (Babylon),thwarted love (Little Mousegrove), and love triumphant (Hind Horn). One of the most popular topics is the conflict between love and family duty, station, or prior commitments:The Cruel Mother, Kempowyne, and Mary Hamilton all show different aspects of this conflict.
Another favourite subject of ballads--and one which has produced some of the finest in the genre--is Treachery and Betrayal. Lord Randal, one of the most popular of Child's ballads, is about a man betrayed by his beloved; Lamkin is about the betrayal of a lord by one of his servants. In Binnorie, a woman lets her sister die so as to get the man she loves.
Although almost all ballads include either love and/or treachery in their subject matter, another element that appears in ballads is the supernatural. There are many different magical elements that appear in ballads: faeries, ghosts, shapechanging, and witchcraft are the most common. Tam Lin and Thomas Rhymer are the two most famous ballads that involve faeries, and The Wife of Usher's Well and Little Sir Hugh are both about women visited by the ghosts of their sons. The Twa Magicians involves shapechanging, as does Kempowyne, and Alison Gross and Willie's Lady are classic ballads about witches. Folklore in the English and Scottish Ballads by Lowry Wimberly is a wonderful book that goes into detail about how the supernatural is used in ballads.
Lords and Ladies populate ballads by the hundreds. Many ballads have a cast composed of nobles, lords, kings and queens. King Willie, Lady Barnard, Lord Randal, Sir Hugh--there are few ballads that don't include at least one lord or lady.
History is also a subject of ballads. Most historical ballads are later period (1600s), and describe local events well-known to the listeners. Mary Hamilton and The Baron O' Brackley are two ballads based, however vaguely, on historical fact. Battles were a popular subject of ballads: The Battle of Otterburn is one of the better-known ballads of this type.