In recent years, the impact of Plant Protection Products (PPPs) on insect pollinator decline has 11 stimulated significant amounts of research, as well as political and public interest. PPP residues have 12 been found in various bee-related matrices, resulting in governmental bodies worldwide releasing 13 guidance documents on methods for the assessment of the overall risk of PPPs to different bee 14 species. An essential part of these risk assessments are PPP residues found in pollen and nectar, as 15 they represent a key route of exposure. However, PPP residue values in these matrices exhibit large 16 variations and are not available for many PPPs and crop species combinations, which results in 17 inaccurate estimations and uncertainties in risk evaluation. Additionally, residue studies on pollen and 18 nectar are expensive and practically challenging. An extrapolation between different cropping 19 scenarios and PPPs is not yet justified, as the behaviour of PPPs in pollen and nectar is poorly 20 understood. Therefore, this review aims to contribute to a better knowledge and understanding of 21 the fate of PPP residues in pollen and nectar and to outline knowledge gaps and future research needs. 22 The literature suggests that four primary factors, the crop type, the application method, the 23 physicochemical properties of a compound and the environmental conditions have the greatest 24 2 influence on PPP residues in pollen and nectar. However, these factors consist of many sub-factors 25 and initial effects may be disguised by different sampling methodologies, impeding their exact 26 characterisation. Moreover, knowledge about these factors is ambiguous and restricted to a few 27 compounds and plant species. We propose that future research should concentrate on identifying 28 relationships and common features amongst various PPP applications and crops, as well as an overall 29 quantification of the described parameters; in order to enable a reliable estimation of PPP residues in 30 pollen, nectar and other bee matrices.