Search and rescue dogs can be generally classified as air scenting, tracking, or trailing. Air scenting dogs primarily use airborne human scent to home in on subjects, whereas tracking and trailing dogs rely on scent deposited on the ground by the subject. Air scenting dogs typically work off-lead, are non-scent discriminating (eg, 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 air scenting dogs, although a typical search area may be 40-160 acres and scent sources can be detected from a distances of 1/4 mile or more.

Although other breeds can be trained for air scenting, the prototypical air scenting dog is a herding (eg, German or Belgian shepherds, border collies) or sporting (eg, golden or Labrador retriever) breed that has a reputation for working closely and in coordination with a human handler. Tracking and trailing dogs are usually scent discriminating and require an uncontaminated scent article from the subject and a relatively undisturbed search area, work on-lead to follow the subject's path, and may use non-human scent (eg, crushed vegetation, disturbed earth) in following the subject's movements.

The effectiveness of tracking and trailing 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 bloodhound is the prototypical tracking dog, although herding and sporting breeds are often successfully trained for either tracking or trailing.

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

In wilderness SAR applications, air scenting 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 (eg, by wildlife).

Disaster dogs are used to locate victims of catastrophic or mass-casualty events (eg, 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 probably rely primarily on air scent, 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 (eg, to search a large area for buried remains) or on-lead (to recover clues from a crime scene). Air scenting 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.