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If you have an emotional support dog and you are attempting to rent an apartment or house, you should tell potential landlords about it. You do not need to disclose the animal's existence when you are applying for housing but you should discuss it when you have been offered the housing.  You can either tell your landlord about your need in person or in a letter. Legally, the landlord has to make a reasonable accommodation for those with a disability. This includes accommodating a prescribed emotional service animal even if the house or apartment usually excludes pets. If your landlord asks for documentation of your disability and your need for a support animal, show them the letter you have gotten from your mental health professional. The landlord has the right to ask for certification that you have a disability, that an animal can help with the condition, and that your animal does indeed help with your condition. Your landlord does not have the right to ask about your specific mental health diagnosis. A letter from your mental health professional should simply state that you have a mental health issue that requires animal support. There are a variety of rules around housing and emotional support animals. Your landlord may not be aware of all of these rules, so gently inform them.  In order to educate your landlord about the rules surrounding emotional support animals you will need to know them yourself. Review federal, state, and local regulations relating to emotional support animals, disability, and housing. The Fair Housing Act is the central US federal law that protects against discrimination in housing. Specifically, it protects those that use assistance animals against discrimination.
Tell a potential landlord about your support animal. Show your landlord documentation of need. Educate your landlord about the rules concerning emotional support animals.