Carlow is the county town of County Carlow, in the south-east of Ireland, 84 km (52 mi) from Dublin. At the 2016 census, it had a combined urban and rural population of 24,272.

The River Barrow flows through the town, and forms the historic boundary between counties Laois and Carlow. However, the Local Government (Ireland) Act 1898 included the town entirely in County Carlow. The settlement of Carlow is thousands of years old and pre-dates written Irish history. The town has played a major role in Irish history, serving as the capital of the country in the 14th century.

The name is an anglicisation of the Irish Ceatharlach. Historically, it was anglicised as Caherlagh, Caterlagh and Catherlagh, which are closer to the Irish spelling. According to logainm.ie, the first part of the name derives from the Old Irish word cethrae ("animals, cattle, herds, flocks"), which is related to ceathar ("four") and therefore signified "four-legged". The second part of the name is the ending -lach.

Some believe that the name should be Ceatharloch (meaning "quadruple lake"), since ceathar means "four" and loch means "lake". It is directly translated as "Four lakes", although, there is seemingly no evidence to suggest that these lakes ever existed in this area.