dog that is professionally trained to guide, protect, or aid its master. Systematic training of guide dogs originated in Germany during World War I to aid blinded (blindness) veterans.

At the age of approximately one year, the guide dog is trained for three to four months to mold its behaviour to its owner's handicap. The dog learns to adjust to a harness, stop at curbs, gauge its owner's height when traveling in low or obstructed places, and disobey a command when obedience will endanger its master. Dogs have also been trained to perform various services for persons with hearing impairments and restricted mobility. Some dogs are trained to assist persons with seizure disorders and to summon help. Although several breeds have been educated for these roles, including Doberman pinschers (Doberman pinscher) and German shepherds (German shepherd), Labrador retrievers and Labrador-golden retriever crosses are the most widely used.