The studies of artificial photosynthesis use biomimetic techniques to replicate the process of natural photosynthesis, which employs abundant resources of sunlight, water, and carbon dioxide to produce oxygen and energy-rich carbohydrates. In this chapter, requirements for successive mimicking of these processes and means for fulfillment, these requirements were formulated. The compounds such as porphyrins or other cyclic tetrapyrroles, coratenoides, ruthenium and zinc complexes, fullerenes, borondipyrromethene, melanin, polyphenylene, go forth, can be light harvesters. Examples of charge separation in artificial donor–acceptor and pairs and photophysical and photochemical processes in dual flourophore-nitroxide molecules were presented and discussed in separate sections. The evolution dioxygen from water in a cluster of transition metals in the biological systems at the absorption of four light quanta of low energy occurs by a sequence of elementary steps: four one-electron steps of oxidation of the manganese complex and, most probably by one four-electron elementary step of O2 evolution (Sect.  3.5.2 ). In approaching mimicking problem, a number of artificial manganese clusters and other transition metal clusters were synthesized and investigated. The reduction, or fixation, of carbon dioxide is a vital process associated with natural and artificial photosynthesis in which can generate hydrocarbon fuels such as formic acid, methanol, carbon monoxide, and methane, with the utilization of hydrogen. Employing of transition metal complexes catalyzed carboxylation reactions with CO2 and carboxylation of preactivated substrates and examples of successive carboxylation were presented The chapter focused on advances in the field of direct carboxylation reactions of C(sp3)–H and C(sp2)–H bonds using CO2 encompassing both transition metal catalysis and base-mediated approach and on applications of electrochemical and photochemical methods.