We give a criterion forq-valent analytic functions in the unit disk to belong toQK, a Möbius-invariant space of functions analytic in the unit disk in the plane for a nondecreasing functionK:[0,∞)→[0,∞), and we show by an example that our condition is sharp. As corollaries, classical results on univalent functions, the Bloch space, BMOA, andQpspaces are obtained.