Series 21 of British television drama The Bill was broadcast from 5 January until 29 December 2005. The series consisted of 106 episodes, making it the series with the highest number of episodes in the show's final decade. This series saw the programme change hands as executive producer of three and a half years, Paul Marquess, stepped down to make way for new producer Jonathan Young. Subsequently, this resulted in the removal of much of the 'soap' feel which was introduced by Marquess, and the main focus turning towards the actual policing aspect of the programme. The majority of this series however remained serialised, with the transition back to single-hander episodes being phased in slowly, following into Series 22.
This series saw the highest number of cast changes in the latter series of the show, with a significant number of key characters axed following the conclusion of several long-running storylines. This series also saw the departure of the show's longest serving cast member at that point, DC Jim Carver (Mark Wingett), who had been with the show since its pilot episode in 1983. As a dedication, a special half-hour 'two-hander' episode was recorded, featuring Carver and Sgt. June Ackland (Trudie Goodwin), who also appeared with Wingett in the show's pilot in '83. This series also featured the final episode of The Bill: Uncovered, a series of special documentaries following the lives and events of particular characters or groups of characters. This particular special, however, was never broadcast in the United Kingdom and was subsequently only shown on terrestrial television in Australia.
The events of the second Sun Hill disaster were also covered in this series, in which DC Ken Drummond was murdered after a petrol-laden van with him inside was driven into the front of the station by crazed PSCO Colin Fairfax. This series also introduced one of the show's longest running storylines, involving the investigation into gangster Pete Larson and Sgt. Smith's subsequent affair with his wife. This storyline was not concluded until Series 22.
On 5 February 2014, the complete series was released on DVD in Australia as a Region 0, playable anywhere in the world.