The Maine Coon is one of the largest domesticated cats. It has a distinctive physical appearance and valuable hunting skills. The breed was popular in cat shows in the late 19th century, but its existence became threatened when long-haired breeds from overseas were introduced in the early 20th century. The Maine Coon has since made a comeback, in 2020 becoming the third most popular pedigree cat breed in the world.

The Maine Coon is a large and sociable cat characterised by a prominent ruff along its chest, robust bone structure, strong jawline, rectangular body shape, an uneven two-layered coat with longer guard hairs over a silky satin undercoat, and a long, bushy tail.

Maine Coons are regarded as "gentle giants" and possess above-average intelligence, making them relatively easy to train. They are known for being loyal to their family and cautious—but not mean—around strangers, but are independent and not clingy. The Maine Coon is generally not known for being a "lap cat," but their gentle disposition makes the breed relaxed around dogs, other cats, and children. Many Maine Coons have a fascination with water and some speculate that this personality trait comes from their ancestors, who were aboard ships for much of their lives. Maine Coons are also well known for being very vocal cats, using trills and chirps to communicate their physical and emotional needs i.e. hunger, thirst, desire to play. Their frequent chirping and trilling is often a sign of happiness and excitement. They also make other loud vocalisations such as yowling or howling.

The Maine Coon was considered the largest breed of domestic cat until the introduction of the Savannah cat in the mid 1980s, and is still the largest non-hybrid breed. On average, males weigh from 18 to 22 lb (8.2 to 10.0 kg), with females weighing from 12 to 15 lb (5.4 to 6.8 kg). The height of adults can vary between 10 and 16 in (25 and 41 cm) and they can reach a length of up to 38 in (97 cm), including the tail, which can reach a length of 14 in (36 cm) and is long, tapering, and heavily furred, almost resembling a raccoon's tail. The body is solid and muscular, which is necessary for supporting their weight, and the chest is broad. Maine Coons possess a rectangular body shape and are slow to physically mature; their full size is normally not reached until they are three to five years old, while other cats take about one year.