You can handle the timing of a spousal hire request in several ways. There is no one right answer for everyone. I used to recommend bringing up the request only once you have an offer and begin formal negotiations. However, I recently spoke with a physical sciences department chair, who shared the following case. His department interviewed a scientist, and during the private interview with the chair the candidate revealed that her partner was also a scientist in a different discipline. She asked whether is was possible to find a position for him. The chair told me he was happy she brought it up at that point in the interview. It didn't impact this search committee's ultimate decision, and it gave the chair time to explore available resources for the partner, if the search committee recommended that the candidate be hired.

So in some cases the question of a spousal hire can be raised during the formal interview. I generally recommend against addressing it in the first communication with the department—that is, in the cover letter—but I have heard of cases where such an early overture has been advantageous for both the candidate and the employer. Whenever you chose to bring it up, you will need to weigh the benefits with the possible negative effects it could have on your candidacy. But if you think creatively, you might even orchestrate a new opportunity for both you and your partner, such as offering to share a faculty line.