If you are a school leaver, then it doesn't have to be very long. The key elements are to include the company you are sending your cover letter to, the job you are applying for, and why you think you would be perfect for the job. Alison Chang, managing director of COREsearch, and Monisa Wan Siu-man, vice-president of the Hong Kong Institute of Human Resource Management, emphasise the importance of spelling and double-checking who you are sending the resume and cover letter to. Because it is so easy to use the search and replace function when you are sending several resumes by e-mail, there are many people who may change the e-mail address, but forget to change the name of the company on the cover letter. A cover letter should highlight who and what you are, not a repeat of the job description, or your resume. But do take a couple of elements of the job description to show what relevant qualities you have.