This by-election was called after Labour TD Patrick Nulty resigned in March.
The former TD said he had sent "inappropriate messages via Facebook", including "inadvertently sending one to a 17-year-old woman" whom he said he had never met.
The 31-year-old said he sent the message "under the influence of alcohol".
It was also reported he sent a message to a woman telling her to wear a skirt the next time she attended his constituency clinic.
This constituency, a three-seater in 2007, gained a seat for the 2011 General Election.
This was recognition of rapid population growth and a significant boundary revision, which saw a population of 12,768 in the Swords-Forrest and Airport areas transfer from Dublin North into Dublin West.
Much of the constituency retains a working-class profile, but there has been large-scale development of new housing estates in recent years, while Castleknock is an established middle-class area.
A big focus on count day will be what happens to the 17,000 votes that Labour got in 2011.
Fís Nua - Daniel William Boyne
A first-time candidate based in Santry, he is a teacher by profession. Fís Nua is also running candidates in each of the three European constituencies – Mathew Damon Wise in Dublin, Cordelia Nic Fhearraigh in Midlands-North-West and Dónal Ó’Ríordáin in South.
Socialist Party - Ruth Coppinger
A member of Fingal County Council since 2003 when she was co-opted to replace Joe Higgins in the Mulhuddart electoral area. Ms Coppinger previously contested the October 2011 by-election for Dublin West. After replacing Joe Higgins as representative for the Mulhuddart ward in 2003, Ms Coppinger was returned as an elected councillor in the 2004 and 2009 local elections.
Fine Gael - Eamonn Coghlan
Former World champion runner, Mr Coghlan was nominated to the Seanad by Taoiseach Enda Kenny in May 2011. Recognised as one of Ireland’s greatest-ever athletes, Mr Coghlan's career began in the 1970s on the American indoor athletics circuit. He competed in three Olympic Games and won the gold medal for Ireland in the 5,000m in the World Championships in Helsinki.
Paul Donnelly - Sinn Féin
Originally from the north inner city, Mr Donnelly joined Sinn Féin in 1995. In 2011, he unsuccessfully contested the Dublin West constituency in both the general election and the subsequent by-election. He currently works with a School Completion Project and Youthreach Centre in Kilmore.
Independent - John Kidd
A fire officers' representative, Mr Kidd contested the October 2011 by-election in Dublin West, polling 311 first preference votes. Reared in the Finglas and Blanchardstown areas, Mr Kidd served in the Defence Forces from 1979 to 1985 and joined the Dublin Fire Brigade in 1990, later becoming a union official at local, national and international levels.
Independent - Seán Lyons
A Blanchardstown-based retired engineering academic. Mr Lyons stood in the 1987, 1992 and 1997 general elections. He was elected as a councillor to Final County Council in 1991.
Fianna Fáil - David McGuinness
Runner-up to Patrick Nulty in the October 2011 by-election, he is a member of Fingal County Council for the Mulhuddart LEA.
In 2009, Mr McGuinness was first elected to Fingal County Council representing Mulhuddart. He attracted 1,203 first preference votes, taking the fourth of five seats. He is Fianna Fáil's youngest county councillor in the country.
Independent - David Hall
First-time candidate, Mr Hall is the founder of the Irish Mortgage Holders' Organisation, an advocacy group for distressed borrowers and those in mortgage arrears. Mr Hall previously took a court challenge against the arrangements on Ireland's promissory notes in 2012. He was previously involved with New Beginnings and also runs Lifeline Ambulances.
Labour - Loraine Mulligan
A researcher with SIPTU and first-time candidate, Ms Mulligan has been Labour Party Chairperson since November 2013. Previously Vice-Chair, she had earlier assumed the duties of Chairperson in June 2013 when Colm Keaveney resigned from the position.
Green Party - Roderic O'Gorman
Mulhuddart-based law lecturer, Mr O'Gorman is contesting a Dáil seat for the fourth time, having stood unsuccessfully in the 2007 and 2011 general elections and the October 2011 by-election.
