There is scant academic research on the challenges encountered by the police when working with the Crown Prosecution Service on rape and serious sexual offence cases; yet this relationship plays a crucial part in improving appropriate case outcomes. This qualitative study aims to further knowledge in this area, using interview data from 50 police officers from four forces across England and Wales, analysed using thematic analysis. Four main challenges with police/CPS working were found: (i) poor communication and relationships, exacerbated by a reliance on electronic systems; (ii) not obtaining early advice; (iii) the CPS driving victim-focused investigations; and (iv) issues with DG6 and disclosure. However, areas of good practice were also found, including: early advice clinics; enhanced early advice; joint police/CPS training/meetings; case progression trackers; and discussions regarding reasonable lines of inquiry.