| Election Name: | 2013 Ynys Môn by-election |
| Type: | parliamentary |
| Country: | Wales |
| Seats For Election: | The Ynys Môn seat in the Welsh Assembly. Triggered by vacation of seat by incumbent |
| Ongoing: | no |
| Previous Election: | 2011 National Assembly for Wales election |
| Previous Year: | 2011 |
| Next Election: | 2016 National Assembly for Wales election |
| Next Year: | 2016 |
| Election Date: | 1 August 2013 |
| Candidate1: | Rhun ap Iorwerth |
| Party1: | Plaid Cymru |
| Popular Vote1: | 12,601 |
| Percentage1: | 58.2% |
| Swing1: | 16.8% |
| Candidate2: | Tal Michael |
| Party2: | Welsh Labour |
| Popular Vote2: | 3,435 |
| Percentage2: | 15.9% |
| Swing2: | 10.3% |
| Candidate4: | Nathan Gill |
| Party4: | UK Independence Party |
| Popular Vote4: | 3,099 |
| Percentage4: | 14.3% |
| Swing4: | New party |
| Candidate5: | Neil Fairlamb |
| Party5: | Welsh Conservative Party |
| Popular Vote5: | 1,843 |
| Percentage5: | 8.5% |
| Swing5: | 20.7% |
| AM | |
| Posttitle: | Subsequent AM |
| Before Election: | Ieuan Wyn Jones |
| Before Party: | Plaid Cymru |
| After Election: | Rhun ap Iorwerth |
| After Party: | Plaid Cymru |
A by-election for the Welsh Assembly constituency of Ynys Môn was held on 1 August 2013,[1] The by-election was triggered following the resignation on 20 June 2013 of its sitting Assembly Member, Ieuan Wyn Jones.[2]
The election was the third Assembly by-election to be held since its formation in 1999, and the first for over seven years (the previous contest being at Blaenau Gwent in June 2006).
Prior to the by-election, the governing Labour Party held exactly half the Assembly seats, meaning a gain for that party (who have held the equivalent seat in the House of Commons since 2001) would have given the Welsh government a two-seat majority.
Six candidates were nominated for the election.[3] [4] [5]