Iodine and astatine radioisotopes are particularly attractive in nuclear medicine since their available isotopes cover all imaging and therapeutic modalities, from SPECT and PET imaging to beta, alpha and Auger electron therapy. Furthermore, their radiolabeling chemistry is highly versatile, being mainly based on covalent chemistry, unlike most other radionuclides that are metals. This makes them easily adaptable for the radiolabeling of a broad range of carrier compounds, from small molecules to large proteins. Iodine and astatine being both neighboring halogens, their radiolabeling chemistry is very similar. Knowledge on At is however limited given its low availability over the past decades and the facts that it exists only as short-lived isotopes, which has long hampered the study of its chemical properties. Nonetheless, recent research has highlighted features that distinguish it from its lighter halogen homologues and late developments open new perspectives with astatine radioisotopes to produce radiopharmaceuticals. In this chapter, the basics of iodine and astatine labeling chemistry are covered in parallel, starting with general principles and then detailing more specific applications and issue. In a first part the main production methods for the most relevant radionuclides, and the corresponding chemicals forms available for radiolabeling chemistry are presented. Radiolabeling reactions, which can be classified as electrophilic or nucleophilic, are introduced and their advantages and drawbacks are discussed. The second part introduces issues encountered in the specific case of proteins radiolabeling and the main strategies available. Finally, a third part discusses the stability issues encountered with iodine and especially At-labeled radiopharmaceuticals and the main approaches under investigation to improve it. The perspectives sections discuss the potential of iodine and astatine radioisotopes in the context of the development of the radiotheranostic modality.