In this chapter we present the methods developed in our laboratory for in vivo imaging of oligonucleotidic aptamers. These methods relate to (i) the labelling of aptamers with fluorine-18, a positron emitter, (ii) Positron Emission Tomography imaging of laboratory animals with [18 F]aptamers and (iii) labelling with fluorescent dyes and optical imaging of aptamers in mice.