Conjugated polymers, which exhibit electrical and optical properties owing to the presence of conjugated π bonds along the polymer backbone, are semiconducting materials of utmost interest. However, their immiscibility in water imposes restrictions on their usage; they are typically processed using toxic and environmentally harmful organic solvents. To address these issues, research has focused on converting conjugated polymers into nanoparticle dispersions in water or alcohols. This strategy not only avoids toxic solvent usage but also enhances application utility. In this article, to provide a comprehensive understanding of conjugated polymer nanoparticles, we introduce two principal approaches for classifying nanoparticle formation strategies and their corresponding experimental methods: with respect to the particle formation mechanisms and their preparation methods; we will discuss six such methods. Then, we review three different applications of the conjugated polymer nanoparticles in the fields of electronics, energy, and bioimaging, associating their requirements for attaining superior device performance with the characteristics of each method, and accordingly discuss methodological perspectives for each application.