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 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...

"Martha: I battle with my textbooks. Doctor: I battle with monsters. Martha: I try to save money. Doctor: I try to save the universe. Martha: I'm gonna be a doctor. Doctor: I am the Doctor. Martha: Well, lets hope this box is big enough for the both of us."

"Martha: I need a guy who's smart. Doctor: Suit and trainers works for me. Martha: Who likes travelling. Doctor: I've been round the block a few times. Martha: Who has a big heart. Doctor: Two of those, actually. Martha: And someone who can make the time. Doctor: Ahh, now that's my speciality."

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.

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.