We prove that any weakly acausal curve Γ in the boundary of anti-de Sitter (2+1)-space is the asymptotic boundary of two spacelike K-surfaces, one of which is past-convex and the other future-convex, for every K ∈ (−∞, −1). The curve Γ is the graph of a quasisymmetric homeomorphism of the circle if and only if the K-surfaces have bounded principal curvatures. Moreover in this case a uniqueness result holds.The proofs rely on a well-known correspondence between spacelike surfaces in anti-de Sitter space and area-preserving diffeomorphisms of the hyperbolic plane. In fact, an important ingredient is a representation formula, which reconstructs a spacelike surface from the associated area-preserving diffeomorphism.Using this correspondence we then deduce that, for any fixed θ ∈ (0, π), every quasisymmetric homeomorphism of the circle admits a unique extension which is a θ-landslide of the hyperbolic plane. These extensions are quasiconformal.Then σ Φ,b is an embedding of Ω ⊆ H 2 onto a convex surface in AdS 3 . If π l is the left projection of the image of σ Φ,b , then π l • σ Φ,b = id, and π r • σ Φ,b = Φ.In fact, given a tensor b satisfying equations (1)-(3), one can still define σ Φ,b by means of equations (5) and (6), and the image of the differential of σ Φ,b is orthogonal to the family of timelike lines {L x,Φ(x) }, but in general dσ Φ,b will not be injective. Actually, given b which satisfies equations (1)-(3), for every angle ρ, also the (1,1)-tensor R ρ • b satisfies equations (1) and (2), where R ρ denotes the counterclockwise rotation of angle ρ. Changing b by postcomposition with R ρ corresponds to changing the surface S to a parallel surface, moving along the timelike geodesics {L x,Φ(x) }. The condition tr b ∈ (−2, 2) (which in general is only satisfied for some choices of b) ensures that σ Φ,b is an embedding.We now restrict our attention to K-surfaces and θ-landslides. A θ-landslide is a diffeomorphism Φ for which there exists b satisfying the conditions of equations (1)-(3) and moreover its trace is constant. More precisely, tr b = 2 cos θ and tr Jb < 0for θ ∈ (0, π). It turns out that θ-landslides are precisely the maps associated to past-convex K-surfaces, for K = −1/cos 2 (θ/2). On the other hand, by means of the map defined in equations (5) and (6), one associates a K-surface to a θ-landslide. Changing b by −b in the defining equations (5) and (6) enables to pass from the K-surface to its dual surface, which is still a surface of constant curvature K * = −K/(K + 1). Hence a θ-landslide is also the map associated with a future-convex K * -surface. A special case of θ-landslides are minimal Lagrangian maps, for θ = π/2. In this case, we get two (−2)-surfaces, dual to one another. It is well known (see [14]) that a minimal Lagrangian map is associated to a maximal surface S 0 in AdS 3 , and that the two (−2)-surfaces are obtained as parallel surfaces at distance π/4 from S 0 . Since in this case tr b = 0, changing b by Jb, one has that Jb is self-adjoint for the hyperbolic metric, and the map σ Φ,J...