In this paper, we present a variational method that recovers both the shape and the reflectance of the Lambertian scene using multiple images. Although we consider only Lambertian surfaces in this paper, the proposed method, which is global and completely model based, is the first and unavoidable stage for reaching a shape and reflectance estimation method for non-Lambertian surfaces. Basically, our method is a multiview stereo/shape from shading algorithm which allows to recover 3D shapes from Lambertian shading with known illumination conditions. Contrary to previous works that deal with a single material object of the constant albedo, our method works for surfaces with non-constant reflectance parameters, in particular with non-constant albedo. In addition, our algorithm is not based on two or more separate steps - shape and reflectance are jointly recovered in a same process. We verified the proposed method using synthetic images. We will extend our method for non-Lambertian surfaces to improve the robustness to non-Lambertian effects.