Nanoplastics (NPs), which we define in this paper as solid plastic particles with the size <1 μm, unintentionally produced from the degradation and fragmentation of larger plastic objects are probably the least known area of plastic litter but are suspected to pose the greatest risk to the environment. However, no NPs have been detected in natural environments to date. This review attempts to provide a critical overview from the polymer science perspective of the relevant scientific literature, which could facilitate finding secondary NPs in natural environments. The information on secondary NPs has been scarce due to the big challenges in sampling, separation, and detection of these nanoscale particles. This review highlights the most important challenges and obstacles and discusses the mechanisms of generation of secondary NPs. It provides also a critical overview on modern instrumentation, newly developed workflows, promising techniques for sampling and sample preparation, and detection methods including spectroscopies (Raman and FT-IR), microscopies (SEM and TEM) and mass spectrometry (GC–MS and ToF–SIMS). We conclude that finding NPs in natural environments is plausible yet uncertain, which drives towards the development of a methodology for collection, separation and identification of NPs in environmental matrices along with a thorough evaluation of the process of formation of secondary NPs, their fate and effects on living organisms and the environment. To find nanoplastics in natural environments it is important to know the process of their formation, their fate, and experimental constraints.