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This monograph presents the state of the art of convexity, with an emphasis to integral representation. The exposition is focused on Choquet's theory of function spaces with a link to compact convex sets. An important feature of the book is an interplay between various mathematical subjects, such as functional analysis, measure theory, descriptive set theory, Banach spaces theory and potential theory. A substantial part of the material is of fairly recent origin and many results appear in the book form for the first time. The text is self-contained and covers a wide range of applications. From the contents: Geometry of convex sets Choquet theory of function spaces Affine functions on compact convex sets Perfect classes of functions and representation of affine functions Simplicial function spaces Choquet's theory of function cones Topologies on boundaries Several results on function spaces and compact convex sets Continuous and measurable selectors Construction of function spaces Function spaces in potential theory and Dirichlet problem Applications

The authors study Sobolev classes of weakly differentiable mappings $f:{\mathbb X}\rightarrow {\mathbb Y}$ between compact Riemannian manifolds without boundary. These mappings need not be continuous. They actually possess less regularity than the mappings in ${\mathcal W}^{1,n}({\mathbb X}\,,\, {\mathbb Y})\,$, $n=\mbox{dim}\, {\mathbb X}$. The central themes being discussed are: smooth approximation of those mappings integrability of the Jacobian determinant The approximation problem in the category of Sobolev spaces between manifolds ${\mathcal W}^{1,p}({\mathbb X}\,,\, {\mathbb Y})$, $1\leqslant p \leqslant n$, has been recently settled. However, the point of the results is that the authors make no topological restrictions on manifolds ${\mathbb X}$ and ${\mathbb Y}$. They characterize, essentially all, classes of weakly differentiable mappings which satisfy the approximation property. The novelty of their approach is that they were able to detect tiny sets on which the mappings are continuous. These sets give rise to the so-called web-like structure of ${\mathbb X}$ associated with the given mapping $f: {\mathbb X}\rightarrow {\mathbb Y}$. The integrability theory of Jacobians in a manifold setting is really different than one might a priori expect based on the results in the Euclidean space. To the authors'surprise, the case when the target manifold ${\mathbb Y}$ admits only trivial cohomology groups $H^\ell ({\mathbb Y})$, $1\leqslant \ell