This essay offers a far-reaching investigation of the role of the grid in structuring urban and architectural space, proposing a reading of the grid not as a form or as a device for representation, but as an agent of the making of space. Beginning with and departing from Rosalind Krauss’ seminal essay on the operative role of the grid in the redefinition of pictorial space in the early 20th century (Grids, 1978), this essay concentrates on the complications of the operation of the grid – the “grid effect” -– when it is employed as an organizing system in architecture and the urban space. Unlike the modern pictorial grid, the “grid effect” does not produce an abstraction from the world, but, inseparable from its implementations, it produces a dynamic and evolving space in the city and in the territory. The potentiality and trans-historical nature of the “grid effect” is explored through a series of cases: from the empirically structured tool of territorial domination of the Roman limitatio, to the never fully implemented grid of the Modern tabula rasa; from the geometrically relentless but socially liberating grids of the architectural utopias of the 1960s, to the contemporary American urban grid, torn open but enclosed in the isolated fragments of its ladders (A. Pope), to the warped surface-space of the soft grid of Zaha Hadid’s recent large scale projects. Key words: Abstract grid. Urban grid. Territorial grid. Adaptable system. Dynamic masterplanning.