Lucy the Yorkshire Terrier, who measures only 5.7 inches tall and weighs 2.5 pounds, may be tiny, but she's got a big reputation. The three-year-old dog was recently named the world's smallest service dog by the Guinness Book of World Records.

According to Guinness, Lucy, who's a certified therapy dog, is the smallest-known working breed on Earth. For the past year, the diminutive pooch has been providing therapy to autistic children and people in hospitals and nursing homes.

Watch Lucy's story below.

[via MSNBC]