A viscount or viscountess is a title used in certain European countries for a noble of varying status.
In many countries a viscount, and its historical equivalents, was a non-hereditary, administrative or judicial position, and did not develop into a hereditary title until much later. In the case of French viscounts, it is customary to leave the title untranslated as vicomte
Etymology
The word viscount comes from Old French visconte (Modern French: vicomte), itself from Medieval Latin vicecomitem, accusative of vicecomes, from Late Latin vice- “deputy” + Latin comes (originally “companion”; later Roman imperial courtier or trusted appointee, ultimately count).
History
During the Carolingian Empire, the kings appointed counts to administer provinces and other smaller regions, as governors and military commanders. Viscounts were appointed to assist the counts in their running of the province, and often took on judicial responsibility. The kings strictly prevented the offices of their counts and viscounts from becoming hereditary, in order to consolidate their position and limit chance of rebellion.
The title was in use in Normandy by at least the early 11th century. Similar to the Carolingian use of the title, the Norman viscounts were local administrators, working on behalf of the Duke. Their role was to administer justice and to collect taxes and revenues, often being castellan of the local castle. Under the Normans, the position developed into a hereditary one, an example of such being the viscounts in Bessin. The viscount was eventually replaced by bailiffs, and provosts.

Robert Gascoyne-Cecil, 7th Marquess of Salisbury … represented South Dorset in the House of Commons, and in the 1990s he was Leader of the House of Lords under his courtesy title of Viscount Cranborne.
As a rank in British peerage, it was first recorded in 1440, when John Beaumont was created Viscount Beaumont by King Henry VI. The word viscount corresponds in the UK to the Anglo-Saxon shire reeve (root of the non-nobiliary, royal-appointed office of sheriff).
Thus early viscounts were originally normally given their titles by the monarch, not hereditarily; but soon they too tended to establish hereditary principalities in the wider sense. They were a relatively late introduction to the British peerage, and on the evening of the Coronation of Queen Victoria in 1838, the Prime Minister Lord Melbourne explained to her why (from her journals):
“I spoke to Ld M. about the numbers of Peers present at the Coronation, & he said it was quite unprecedented. I observed that there were very few Viscounts, to which he replied “There are very few Viscounts,” that they were an old sort of title & not really English; that they came from Vice-Comites; that Dukes & Barons were the only real English titles;—that Marquises were likewise not English, & that people were mere made Marquises, when it was not wished that they should be made Dukes.”
United Kingdom
A viscount is the fourth rank in the British peerage system, standing directly below an earl and above a baron (Lord of Parliament in Scotland). There are approximately 270 viscountcies currently extant in the peerages of the British Isles, though most are secondary titles.
In British practice, the title of a viscount may be either a place name, a surname, or a combination thereof: examples include the Viscount Falmouth, the Viscount Hardinge and the Viscount Colville of Culross, respectively.
An exception exists for Viscounts in the peerage of Scotland, who were traditionally styled “The Viscount of [X]”, such as the Viscount of Arbuthnott. In practice, however, very few maintain this style, instead using the more common version “The Viscount [X]” in general parlance, for example Viscount of Falkland who is referred to as Viscount Falkland.
A British viscount is addressed in speech as Lord [X], while his wife is Lady [X], and he is formally styled “The Right Honourable The Viscount [X]”. The children of a viscount are known as The Honourable [Forename] [Surname], with the exception of a Scottish viscount, whose eldest child may be styled as “The Honourable Master of [X]”.
Ireland
The title of viscount (Irish: bíocunta) was introduced to the Peerage of Ireland in 1478 with the creation of the title of Viscount Gormanston, the premier viscountcy of Britain and Ireland, held today by Nicholas Preston, 17th Viscount Gormanston. Other early Irish viscountcies were Viscount Baltinglass (1541), Viscount Clontarf (1541), Viscount Mountgarret (1550) and Viscount Decies (1569).
Use as a courtesy title
A specifically British custom is the use of viscount as a courtesy title for the heir of an earl or marquess. The peer’s heir apparent will sometimes be referred to as a viscount, if the second most senior title held by the head of the family is a viscountcy. For example, the eldest son of the Earl Howe is Viscount Curzon, because this is the second most senior title held by the Earl.
However, the son of a marquess or an earl can be referred to as a viscount when the title of viscount is not the second most senior if those above it share their name with the substantive title. For example, the second most senior title of the Marquess of Salisbury is the Earl of Salisbury, so his heir uses the lower title of Viscount Cranborne.
Sometimes the son of a peer can be referred to as a viscount even when he could use a more senior courtesy title which differs in name from the substantive title. Family tradition plays a role in this. For example, the eldest son of the Marquess of Londonderry is Viscount Castlereagh, even though the Marquess is also the Earl Vane.
On occasion, the title of viscount may be the courtesy title used for the grandson of a duke, provided that he is the eldest son of the duke’s eldest son. This is because the eldest son of the duke will be given the second highest title of his father (marquess or earl), and so the third-highest is left for his eldest son. It is possible for the great-grandson of a duke to hold the courtesy title of viscount if the duke’s eldest son has the courtesy title marquess and his eldest son, in turn, uses the title of earl.