The content of this review article will be focussed on photochemically induced electron-transfer reactions (PET) of donor-acceptor systems. Following a brief introduction new developments of photoreactions between donor and acceptor molecules will be presented. The modes of these reactions (substitution and cycloaddition) and even the stereoselectivities of cycloadditions can be controlled by the photoinduced charge separation. Examples of the currently intense growing area of the radical ion chemistry, which are of synthetic interest, will be presented in the second main part. 1. Introduction 2. General Remarks 3. Donor-Acceptor Reactions 3.1. Arenes 3.1.1. Acceptor-Substituted Arenes 3.1.2. Donor-Substituted Arenes 3.2. Carbonyl Compounds 3.3. Iminium Salts 3.4. Organic Halides 4. Radical Ion Reactions 4.1. Alkenes and Related Compounds 4.1.1. Isomerization and Rearrangements 4.1.2. Dimerization and Cycloaddition 4.1.3. Nucleophilic and Electrophilic Additions 4.2. Strained Ring Systems 4.3. Arenes (Substitution and Reduction) 4.4. Organic Anions and Carbenium Ions 4.5. PET Induced Cleavage 4.6. Electron-Transfer Photooxygenations 5. Concluding Remarks