Pillarisation (a calque from the Dutch: verzuiling [vɛrˈzœylɪŋ] ^ⓘ) is the vertical division of a society into separate groups, or pillars (Dutch: zuilen), organized along religious, socio-economic, and ideological lines. The phenomenon is most closely associated with historical examples in the Netherlands and Belgium.

In a pillarised society, each pillar maintains its own institutions and social organizations. These may include newspapers, broadcasting organisations, political parties, trade unions, farmers' associations, banks, shops, schools, hospitals, universities, scouting groups, and sports clubs. This segregation results in limited social interaction between members of different pillars. In the Netherlands, society was historically divided into four main pillars: Catholic, Protestant, Socialist, and Liberal. The system allowed each community to maintain its own institutions and lifestyle, minimizing conflict among groups. Inter-pillar social relationships, including marriage and friendship, were generally discouraged.

Pillarisation also reflected the social awareness of groups that had been marginalized or disadvantaged during the 19th century by the liberal bourgeoisie, which promoted Enlightenment ideals as universal norms. The system began to decline in the 1960s and 1970s, as social and political barriers weakened. However, traces of pillarisation remain visible in contemporary Dutch political parties, media institutions, and in certain conservative religious communities, such as those in the Dutch Bible Belt.

Comparable systems of social segmentation have been identified in other countries, including Northern Ireland, Switzerland, Austria, Cyprus, Lebanon, and Malaysia.

The Netherlands historically developed at least three main social pillars: Protestant, Catholic, and social democratic. Pillarisation in the country was initiated in the late 19th century by Abraham Kuyper, a theologian and politician associated with the Anti-Revolutionary Party (ARP), a Christian democratic and neo-Calvinist (gereformeerd) organization connected to the Reformed Churches in the Netherlands. The movement was grounded in Kuyper’s philosophy of sphere sovereignty,^{[failed verification]} which held that distinct areas of life—such as religion, politics, and education—should operate autonomously within their own spheres.

Although pillarisation declined during the 1960s and 1970s, its influence remains evident in Dutch society, particularly in communities outside the Randstad region, where aspects of pillarised life persist alongside broader participation in civil society.

The Catholic pillar was historically the most tightly organized, reflecting the Catholic clergy’s encouragement of collective organization within confessional institutions. The conservative Protestant pillar and the socialist pillar, which primarily represented the proletariat, were also highly cohesive. The Christian Historical Union (CHU), founded in 1908 and associated with the Dutch Reformed Church (hervormd), aligned itself with the Protestant pillar shaped by the ARP rather than creating a separate structure.

Those outside the three main pillars—primarily middle- and upper-class latitudinarian Protestants and atheists—were sometimes grouped into a liberal or "general" pillar. However, ties among liberal organizations were considerably weaker than within the other pillars. Liberals generally opposed the voluntary segregation of society and often denied that a liberal pillar existed. The political parties commonly linked with this group included the Free-thinking Democratic League (VDB) and the Liberal State Party (LSP). Smaller groups such as communists, humanists, and Protestant fundamentalists also established their own organizations, though on a much smaller scale.