Molecular imaging shows promise as a useful tool to aid drug discovery and development and also to provide important prognostic and predictive diagnostic information affecting patient management in the clinic. However, the use of molecular imaging diagnostically is not widely adopted, in part due to the lack of suitable targeting agents. Affibody molecules are a class of small and very stable protein domains, which can be used to selectively address a wide range of protein targets. Their small size enables high contrast radionuclide imaging and they can be produced by conventional peptide synthesis methods. Their potential utility in molecular imaging is highlighted in a large number of animal studies using anti-HER2 Affibody tracers and has recently been validated in breast cancer patients with HER2-expressing metastases. The therapeutic efficacy of the Affibody molecules in this indication was demonstrated in preclinical models using a targeted radionuclide as the effector function. This review will focus on the recent use of Affibody molecules for molecular imaging and their application for radioimmunotherapy.