SIPTU (/ˈsɪptuː/; Services, Industrial, Professional and Technical Union; Irish: An Ceardchumann Seirbhísí, Tionsclaíoch, Gairmiúil agus Teicniúil) is Ireland's largest trade union, with around 200,000 members. Most of these members are in the Republic of Ireland, although the union does have a Northern Ireland District Committee. Its head office, Liberty Hall, is in Dublin, and the union has five industrial divisions, three in the private sector and two in the public sector. SIPTU is affiliated to the Irish Congress of Trade Unions.

The Union has its roots in two separate trade unions both founded by the trade union leader and socialist activist James Larkin; the Irish Transport and General Workers' Union and the Federated Workers' Union of Ireland. The two unions merged in 1990 to create SIPTU. The merge was first proposed in the 1950s, and almost happened in 1969.

SIPTU is a general union which organises across the public and private sectors in Ireland and has large numbers of members working in construction, health, education, transport and manufacturing. It has a long-term commitment to delivering social solidarity and has developed a leadership role in the areas of rights for unemployed persons, people with disabilities and older persons. The union, as part of promoting fairness at work and justice in society, includes migrant workers in Ireland and campaigns on the twin issues of the exploitation of migrant workers, particularly those from Poland, Latvia and Lithuania, and the consequent displacement of Irish workers from employment.

The union established an Organising Unit in 2004 and its former president, Jack O'Connor, set as his objective the transformation of SIPTU - hitherto firmly committed to a servicing agenda - into an organising union.^[2]

Since its formation, several smaller unions have merged into SIPTU:^[2]

1991: Irish National Painters' and Decorators' Trade Union

1993: Irish Writers' Union

1997: Automobile, General Engineering and Mechanical Operatives' Union

1998: Irish Print Union, Marine, Port and General Workers' Union, Professional Footballers' Association of Ireland

2002: Musicians' Union of Ireland

• List of trade unions