We consider the subcritical SQG equation in its natural scale invariant Sobolev space and prove the existence of a global attractor of optimal regularity. The proof is based on a new energy estimate in Sobolev spaces to bootstrap the regularity to the optimal level, derived by means of nonlinear lower bounds on the fractional laplacian. This estimate appears to be new in the literature, and allows a sharp use of the subcritical nature of the L ∞ bounds for this problem. As a byproduct, we obtain attractors for weak solutions as well. Moreover, we study the critical limit of the attractors and prove their stability and upper-semicontinuity with respect to the strength of the diffusion. THEOREM 1.1. Let γ ∈ (1, 2) be fixed, and assume that f ∈ L ∞ ∩ H 2−γ . The dynamical system S γ (t) generated by (SQG γ ) on H 2−γ possesses a unique invariant global attractor A γ , bounded in H 2−γ/2 , and therefore compact in H 2−γ . In particular,Another important feature of the attractors A γ is their stability with respect to the parameter γ, as γ → 1 + . Namely, the following uniform estimates and upper semicontinuity result hold.2000 Mathematics Subject Classification. 35Q35, 35B41, 35B45.