The 2017–18 Primeira Liga (also known as Liga NOS for sponsorship reasons) is the 84th season of the Primeira Liga, the top professional league for Portuguese association football clubs. Benfica are the three-time defending champions, having won their fourth consecutive league title in the previous season.
Eighteen teams will compete in the league – the top sixteen teams from the previous season, as well as two teams promoted from the LigaPro.
Portimonense became the first club to be promoted on 23 April 2017 and will play in Primeira Liga for the first time since the 2010–11 season. On 21 May 2017, after a 2–1 win in Azores against Santa Clara, they were crowned champions. The other team promoted were runners-up Desportivo das Aves, following a 2–2 draw against União da Madeira on 30 April 2017. This will mark the return of the Vila das Aves' team to the top flight after a 10-season absence.
The two promoted clubs replaced Nacional and Arouca. Nacional confirmed their relegation on 5 May 2017, 15 years after their promotion, when Moreirense, who were also struggling to escape relegation, beat Braga. On the last matchday, Arouca's 4–2 defeat against Estoril sealed their relegation, four seasons after having been promoted for the first time to Primeira Liga.