Guide dogs are assistance dogs trained to lead blind and visually impaired people around obstacles.

Although the dogs can be trained to navigate various obstacles, they are partially (red-green) color blind and are not capable of interpreting street signs. The human half of the guide dog team does the directing, based upon skills acquired through previous mobility training. The handler might be likened to an aircraft's navigator, who must know how to get from one place to another, and the dog is the pilot, who gets them there safely.

In several countries, guide dogs, along with most service and hearing dogs, are exempt from regulations against the presence of animals in places such as restaurants and public transportation.

References to guide dogs date at least as far back as the mid-16th century; the second line of the popular verse alphabet "A was an Archer" is most commonly "B was a Blind-man/Led by a dog" In the 19th century verse novel Aurora Leigh by Elizabeth Barrett Browning, the title character remarks "The blind man walks wherever the dog pulls / And so I answered."

A guide is a person who leads anyone through unknown or unmapped country. This includes a guide of the real world (such as someone who conducts travellers and tourists through a place of interest), as well as a person who leads someone to more abstract places (such as to knowledge or wisdom).

There are many variants of guides in this context, and guides are often employed in any aspect of travel or adventure, or wherever there is an advantage to the client in terms of knowledge provided in improving the overall travel experience or making the client feel more safe due to the presumed expertise of the guide.
These days guides will normally possess an area and field-specific qualification usually issued and/or recognised by the appropriate Guide's Association or licensing authority. However this is not always the case, and it is advisable for travellers paying a premium to go on an organised tour or journey because they think this will mean they will have a better experience to check the guide's qualifications beforehand.
Explorers in the past venturing into territory unknown by their own people invariably hired guides. American West explorers Lewis and Clark hired a Shoshone Indian woman Sacagawea, and Wilfred Thesiger hired guides in the deserts that he ventured into, such as Kuri on his journey to the Tibesti Mountains in 1938.
Aside from knowing the way or the area geographically, modern guides are usually hired to act as interpreters for those travellers who do not speak the local language and provide cultural, historical or other information on the area visited. Travel companies organising tours of large groups often have a guide or tour leader accompany the group. They might also be trained in First Aid and have other skills that reduce the risk for the tour operator to conduct these tours or the travel agency selling them.
Here are some examples of guide professions:

The domestic dog (Canis lupus familiaris), is a subspecies of the gray wolf (Canis lupus), a member of the Canidae family of the mammilian order Carnivora. The term "domestic dog" is generally used for both domesticated and feral varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in human history. The word "dog" may also mean the male of a canine species, as opposed to the word "bitch" for the female of the species.

The present lineage of dogs was domesticated from gray wolves about 15,000 years ago. Remains of domesticated dogs have been found in Siberia and Belgium from about 33,000 years ago. None of these early domestication lineages seem to have survived the Last Glacial Maximum. Although mDNA suggest a split between dogs and wolves around 100,000 years ago no specimens predate 33,000 years ago that are clearly morphologically domesticated dog.

Dogs' value to early human hunter-gatherers led to them quickly becoming ubiquitous across world cultures. Dogs perform many roles for people, such as hunting, herding, pulling loads, protection, assisting police and military, companionship, and, more recently, aiding handicapped individuals. This impact on human society has given them the nickname "Man's Best Friend" in the Western world. In some cultures, dogs are also source of meat. In 2001, there were estimated to be 400 million dogs in the world.