For many with pets, renting an apartment is more difficult than it should be. It can depend on the market at a given time in a given locale, landlord's past experiences, and the ability of prospective renters to represent themselves and their pets as responsible tenants.
There are benefits to renting to people with animals. Studies show that renters with pets are more likely to stay in pet-friendly apartments for longer periods of time. Being open to tenants with pets widens the poll of potential people to rent the property. Responsible tenants with pets will also likely have a higher level of commitment to the property, the community and the neighborhood. Landlords seeking responsible renters can find that responsible tenants with pets can make great long term residents.
People who have pets and are seeking an apartment can make this process easier by allowing enough time for the search and having documentation about pets, including veterinary records, behavior classes, and any other information to demonstrate responsible pet guardianship. Some people will have letters of recommendation from past landlords available (with phone numbers) and offer to pay the full legally allowed security deposit for damage. Offering to introduce your animals(s) to a prospective landlord can be helpful. some people also have had success working with Realtors who advertise as pet friendly and looking in sections of a city that are know to be welcoming to pets. When you do land a rental be sure to live up to the standard as a highly responsible tenant.
The Massachusetts Animal Coalition (MAC) has more information for both landlords and renters at massanimalcoalition.org (click on Resources). This includes model guidelines and agreements, checklists and other valuable tools.