Dogs older than 6 months need to be licensed before April 1 of each year. You can think of this license as the equivalent of your ID! For the city of Boston, the application costs $15 for a neutered/spayed dog and $30 for an intact dog. The fine for an unlicensed dog is $50. Fees vary slightly by city so make sure to check your specific city.
You can submit your application online in most cities. A select few still require a mailed submission. To apply, you’ll need to provide a copy of your dog’s current rabies certificate (your vet will be able to provide this for you) and proof of them being spayed or neutered. You'll have to renew it once a year for the duration of your dog's lifetime but you only have to provide your dog's license number so it's quick and easy after your first time.
Find your city in the list below to visit their online portal to register your dog.
Links by city