The Riemann Mapping Theorem states the existence of a conformal homeomorphism ϕ of a simply connected plane domain Ω ⊂ C with non-empty boundary onto the unit disc D ⊂ C. In the first part of the paper, we study embeddings of Sobolev spacesinto weighted Lebesgue spaces Lq(Ω, h) with a "universal" weight that is the Jacobian of ϕ; i. e., h(z) := J(z, ϕ) = |ϕ ′ (z)| 2 . Weighted Lebesgue spaces with such weights depend only on the conformal structure of Ω. For this reason, we call the weights h(z) conformal weights. In the second part of the paper, we prove compactness of embeddings of Sobolev spacesWith the help of Brennan's Conjecture, we extend these results to the Sobolev spaces • W 1 p (Ω). In this case, q depends on p and the integrability exponent for Brennan's Conjecture. The last part of the paper is devoted to applications to elliptic boundary value problems.