The concept of utopia is highly contested and, in many respects, problematic, but it remains indispensable for the prefiguration of an alternative society, for moving beyond a system of power perceived as unjust, oppressive, obscure. Utopia is problematic for its polysemic meaning (as illusion, the impossibility to achieve, a critical tool, a project, a dream), and for its controversial link with (but also distinction from) the concept of ideology. It is problematic if considered in its connection to constructions of imaginary and indeterminate worlds that are not anchored to reality, material conditions and social subjects, nor to concrete possibilities of transformation. And yet utopia is indispensable in its function of contestation. Moreover, the concept of utopia is indispensable as a possible horizon for real historical processes; it sustains the idea of a movement of history towards a future that is paradigmatically valid to guide present action, together with the very possibility of building an alternative society. In fact, utopias are essential in providing materials for the imagination and design of another world, and of a non-capitalist society in particular. Finally, utopia is indispensable in its allusion to a ‘principle of hope’, as Ernst Bloch would define it, capable of projecting the present into the open time of the future, of the possible-future.