All dogs bark under certain circumstances; for example, when someone is at the door or when the dog wants to be fed. However, if your neighbour has a dog that barks all the time, you are within your rights to complain. If your neighbour is at work during the times when the dog is barking, she might not even be aware of the problem. Your letter might be the first indication that she needs to correct the dog's behaviour.
Type your name and address. For a complaint to be effective, identify yourself or it might seem like bullying to the recipient. Skip a space and type the date. You need a record of the dates of the correspondence in case you take the matter to court.
Skip another line, and type the recipient's name and address on separate lines, and skip an additional line. If you don't know the recipient's name, make an effort to find out by asking other neighbours or checking the name on the letterbox. A complaint written to a particular person is more effective than a general complaint.
Type the salutation: "Dear Mr./Ms. (Recipient's name)" followed by a colon. If you were unsuccessful at finding a name, type "Dear Resident at (address)" followed by a colon. You need to identify the recipient in some way in case you decide to sue later.
Explain the matter right away in a polite tone. Remember that the neighbour might not know that his dog is barking, so being rude could be inappropriate. Be specific about the problem; when is the dog barking? How is the barking disturbing you?
Concede that you are aware that all dogs bark under certain circumstances, but that you believe her dog's barking is excessive and she should be aware of it so she can correct the matter. Write with the assumption that she wasn't aware of the problem and that she will want to correct the situation. Even if she did know about the situation, she will appreciate your effort to be polite and may be more likely to accommodate your needs.
Thank your neighbour for his time. Close the letter by typing "Sincerely," and skip three lines. Type your name. Print the letter and sign your name above your typed name. Make a copy of the letter for your records, and mail the original with signature confirmation so you have evidence that the neighbour received your letter.
If the recipient doesn't fix the problem, send another letter explaining that the problem has not been fixed and that if the neighbour doesn't take more-serious measures to silence her dog that you will call the police and file a noise complaint. In this follow-up letter, be polite but firm. Then, call the police if you need to the next time the dog starts barking uncontrollably.