This chapter discusses considerations on the choice of different labels suitable for various detection and imaging methods. It describes labeling methods of protein therapeutics in terms of direct versus indirect methods and in terms of radiohalogens (e.g., radioiodine), trivalent cation radiometals (e.g., indium, copper, and zirconium), and fluorophores. The chapter provides a guide for scientists to find the optimal combination of labeling techniques and labels suitable for pharmaceutical application. The chapter also discusses the advantages and the limitations of the labeling method. It emphasises on the use of numerous imaging techniques for assessing the pharmacokinetics (PK) and biodistribution of biologic proteins, with a focus on positron emission tomography (PET) and single‐photon emission computed tomography (SPECT) and a brief discussion of the role of optical imaging (OI) in this application. Biodistribution studies for biologics are routinely carried out using radioactive iodine isotopes.