Injectivity and Projectivity in Analysis and Topology

We give new proofs for many injectivity results in analysis that make more careful use of the duality between unital abelian C*-algebras and compact Hausdorff spaces. We then extend many of these results to incorporate group actions. Our approach uses only elementary topological constructions and eliminates the need for results from the theory of Boolean algebras and AW*-algebras that were used in earlier proofs.