When Two Worlds Collide (TV story)

 was a narrative trailer advertising the third series of Doctor Who and the introduction of Martha Jones as a companion.

Prior to the trailers release two 10 second teasers, one focused on the Tenth Doctor and the other on Martha, began airing from 9 March 2007.

On 22 March 2007, a second trailer began airing.

The tagline for the marketing campaign was When two worlds collide, anything can happen...

Cast
DWMSE 17 revealed the following credits:
 * The Doctor - David Tennant
 * Martha Jones - Freema Agyeman
 * Voice-over - Jo Butler

Crew
No crew were credited for this trailer.

Uncredited crew
DWMSE 17 revealed the following credits:
 * Director - Richard Senior
 * Producer - Matt Scarff
 * Creative director - Ruth Shabi
 * Marketing - Georgina Pickard
 * Production manager - Sally Anglin
 * Production co-ordinator - Theresa Murphy
 * Team Assistant - Shelley Bradley
 * 1st assistant director - Paul Bennett
 * 3rd assistant director - Anna Evans
 * Director of photography - Paul Barton
 * Focus puller - Matt Dudding
 * Clapper loader - Stephen Andrews
 * Gaffer - Peter Chester
 * Electricians - Gary Owen, Chris Davies
 * Sound recordist - Ron Bailey
 * Overlay Operator - Sylvester Weekes
 * Grip - Dai Hopkins
 * Grip Assistant - Llyr Williams
 * Production designer - Edward Thomas
 * Costume - Louise Page
 * Make-up - Barbara Southcott, Steven John
 * Online Editor (Clips) - Pete Fehervari
 * Visual effects - Nial Brown
 * Graphic designer - Matthew Piper
 * Sound design - Paul Ostwind

Other series 3 trailers
There were also other non-narrative clip based trailers advertising the third series.

Christmas special
On 2 December 2006, a 40 second BBC One Christmas Drama trailer began airing on television, it featured several clips from Doctor Who. There was also a 60 second version, and the music used was "Christmas with the Devil" by Spinal Tap.

On 12 December, the first 20 second trailer for The Runaway Bride was released online as part of the Adventure Calendar on the Doctor Who website, and began airing on BBC One from 16 December. A second 30 second trailer began airing on 19 December, and again was included in the Adventure Calendar on the Doctor Who website.

Main series
An 85 second trailer began airing on the BBCi service from 29 March 2007, it had been created for the press launch on 21 March 2007, it featured the tagline When two worlds collide the adventure begins, and marked the first use of the music cue "All the Strange, Strange Creatures". It featured clips from every episode of Series 3 apart from The Shakespeare Code. It was also released online on the Doctor Who website and YouTube.

The series finale trailers that began airing from 18 June 2007, featured the "Vote Saxon" checkbox, and used the diegetic sound of the Master's "drumming" instead of music. The episode 13 trailer also included the tagline The Master has returned.

Home video releases

 * The complete set of teasers and trailers were included on the Doctor Who: The Complete Third Series DVD box set released on 5 November 2007.