Search and rescue (SAR) dogs detect human scent. Although the exact processes are still researched, it may include skin rafts (scent-carrying skin cells that drop off living humans at a rate of about 40,000 cells per minute), evaporated perspiration, respiratory gases, or decomposition gases released by bacterial action on human skin or tissues.

Search and rescue dogs are typically worked by a small team on foot, but can be worked from horseback.

From their training and experience, search and rescue dogs can be classified broadly as either airscenting dogs or trailing (and tracking) dogs. They also can be classified according to whether they "scent discriminate", and under what conditions they can work. Scent discriminating dogs have proven their ability to alert only on the scent of an individual person, after being given a sample of that person's scent. Non-scent discriminating dogs alert on or follow any scent of a given type, such as any human scent or any cadaver scent. SAR dogs can be trained specifically for rubble searches, for water searches, and for avalanche searches.

Airscenting dogs primarily use airborne human scent to home in on subjects, whereas trailing dogs rely on scent of the specific subject. Airscenting dogs typically work off-lead, are non-scent discriminating (e.g., locate scent from any human as opposed to a specific person), and cover large areas of terrain. These dogs are trained to follow diffused or wind-borne scent back to its source, return to the handler and indicate contact with the subject, and then lead the handler back to the subject. Handler technique, terrain, environment (vegetation), and atmospheric conditions (wind speed and direction, temperature, humidity, and sky conditions) determine the area covered by airscenting dogs, although a typical search area may be 40-160 acres and scent sources can be detected from a distance of 1/4 mile or more. Although other breeds can be trained for airscenting, the prototypical airscenting dog is a herding (e.g., German or Belgian shepherds, Border Collies) or sporting (e.g., Golden or Labrador retrievers) breed that has a reputation for working closely and in coordination with a human handler.

Trailing dogs are scent discriminating and require a scent article from the subject, work on-lead or off lead to follow the subject's path. Tracking dogs follow ground disturbance using non-human scent (e.g., crushed vegetation, disturbed earth) in following the subject's movements as in sporting type events such as AKC Tracking and Schutzhund Tracking. The effectiveness of tracking dogs is highly dependent upon the terrain (some surfaces, such as grass, retain scent better than others, such as pavement), the age of the trail (fresher is easier to follow), the path (the dog is most likely to lose the trail if there are sharp turns or changes in direction), and the number of contaminating paths that cross the subject's path. The scent specific Trailing Trained Dog can follow a trail that may be very aged, from hours to days old, because of various factors the least of which is that the scent can be anywhere in the environment and not necessarily on the ground. The bloodhound is the prototypical Trailing dog, although herding and sporting breeds are often successfully trained for either trailing or tracking with trailing being the optimum.

In addition to these types of dogs, some teams cross train dogs in both trailing and airscenting and use them as scent specific "area search dogs". Typically these dogs are worked in an area that an airscent dog would work, but are capable of ignoring other search teams and other people in or near the assigned search area. When deployed this way, these airscenting dogs require a scent article as does a trailing dog.

Specific applications for SAR dogs include wilderness, disaster, cadaver, avalanche, and drowning search and rescue or recovery.

In wilderness SAR applications, airscenting dogs can be deployed to high-probability areas (places where the subject may be or where the subject's scent may collect, such as in drainages in the early morning) whereas tracking/trailing dogs can be deployed from the subject's last known point (LKP) or the site of a discovered clue. Handlers must be capable of bush navigation, wilderness survival techniques, and be self-sufficient. The dogs must be capable of working for 4–8 hours without distraction (e.g., by wildlife).

Disaster dogs are used to locate victims of catastrophic or mass-casualty events (e.g., earthquakes, landslides, building collapses, aviation incidents). Many disaster dogs in the US are trained to meet the Federal Emergency Management Agency K9 standards for domestic or international deployment; advanced agility and off-lead training are prerequisites reflecting the nature of these dogs' application. Disaster dogs rely primarily on airscent, and may be limited in mass-casualty events by their inability to differentiate between survivors and recently-deceased victims.

Human Remains Detection (HRD) or cadaver dogs are used to locate the remains of deceased victims. Depending on the nature of the search, these dogs may work off-lead (e.g., to search a large area for buried remains) or on-lead (to recover clues from a crime scene). Airscenting and tracking/trailing dogs are often cross-trained as cadaver dogs, although the scent the dog detects is clearly of a different nature than that detected for live or recently-deceased subjects. Cadaver dogs can locate entire bodies (including those buried or submerged), decomposed bodies, body fragments (including blood, tissues, hair, and bones), or skeletal remains; the capability of the dog is dependent upon its training.