Marquis (also Marques), Marchioness
Created 1385. Rank above Earl, below a Duke.

Earl (Count), Countess
Created c.800. Chief royal representative in the shires, replacing the AngloSaxon equivalent, "ealdorman".

Viscount, Viscountess
Created 1440. Rank in peerage below Earl, above Baron. Originally, a viscount was a sheriff of a shire (county) and was the Earl's deputy.

Baron, Baroness
Created c.1066. Lowest rank of the peerage, usually applied to tenants-in-chief, the holders of land granted to them directly by the monarch.

Baronet
Created 1611. A special hereditary rank, above Knight and below Baron, introduced by James I for the purpose of raising money for the supression of the rebellion in Ulster. Baronets were required to pay £1,080 for the privilege of their rank.

Lord
Not a title, per se, but a form of address for a marquis, an earl, a viscount, a baron, a younger son of a duke or marquis, or a bishop.