This Feature Article summarizes the recent advances of water-soluble fluorescent conjugated polyelectrolytes (CPEs) in bioimaging. Apart from a brief overview of traditional linear CPEs, a special emphasis is placed on CPEs that can self-assemble into or are born with three-dimensional nano-architectures, including grafted CPEs, hyperbranched CPEs, and polyhedral oligomeric silsesquioxanes(POSS)-based CPE derivatives. These CPEs naturally form nanoparticles with sizes ranging from 3 to 100 nm in aqueous media, and possess reactive functional groups for bioconjugation or complexation with desired biorecognition elements. The tunable size, low cytotoxicity, good photostability, and ease of surface modification ultimately enable these CPEs with wide applications in in vitro intracellular protein sensing, cell detection, in vivo cell imaging and drug tracking. Moreover, traditional linear CPEs can be transformed into uniform nanoparticles by complexation with oppositely charged biomolecules to allow for cell detection and in situ drug release monitoring. The work featured herein not only reveals the important molecular design principles of CPEs for different imaging tasks, but also highlights the promising directions for the further development of CPE-based imaging materials.