Polymer solar cells, a highly innovative research area for the last decade until today, are currentlymaturing with respect to understanding of their fundamental processes of operation. The increasing interestof the scientific community is well reflected by the—every year—dynamically rising number ofpublications. This chapter presents an overview of the developments in organic photovoltaics employingconjugated polymers as active materials in the photoconversion process. Here the focus is on differentiatingbetween the various material systems applied today: polymer–fullerene, polymer–polymer, polymer–nanoparticlehybrids, and polymer–carbon nanotube combinations are reviewed comprehensively.