Peerage of England
The ranks of the English peerage are, in descending order, Duke, Marquess, Earl, Viscount, and Baron. While most newer English peerages descend only in the male line, many of the older ones (particularly older baronies) can descend through females. Under English inheritance law all daughters are co-heirs, so many older English peerage titles have fallen into abeyance between various female co-heirs.
Forms of address in the United Kingdom
"Eldest sons of dukes, marquesses and earls use their father's most senior subsidiary title as courtesy titles: note the absence of "The" before the title. If applicable, eldest sons of courtesy marquesses or courtesy earls also use a subsidiary title from their (great) grandfather, which is lower ranking than the one used by their father. Eldest daughters do not have courtesy titles; all courtesy peeresses are wives of courtesy peers."
"(Heirs-apparent and heirs-presumptive of Scottish peers use the titles "Master" and "Mistress"; these are substantive, not courtesy titles. If, however, the individual is the eldest son of a Duke, Marquess or Earl, then he uses the appropriate courtesy title, as noted above.)"