An auto mechanic or motor mechanic (Australian English) is a mechanic who specialises in automobile maintenance, repair, and sometimes modification. A mechanic may be knowledgeable in working on all parts of a variety of car makes or may specialize either in a specific area or in a specific make of car. In repairing cars, their main role is to diagnose the problem accurately and quickly. They often have to quote prices for their customers before commencing work or after partial disassembly for inspection. The mechanic uses both electronic means of gathering data as well as their hands, ears, eyes and nose. Their job may involve the repair of a specific part or the replacement of one or more parts as assemblies.

Basic vehicle maintenance is a fundamental part of a mechanic's work in some countries, while in others they are only consulted when a vehicle is already showing signs of malfunction. Preventative maintenance is also a fundamental part of a mechanic's job, but this is not possible in the case of vehicles that are not regularly maintained by a mechanic. One misunderstood aspect of preventative maintenance is scheduled replacement of various parts, which occurs before failure to avoid far more expensive damage. Because this means that parts are replaced before any problem is observed, many vehicle owners will not understand why the expense is necessary.
With the rapid advancement in technology, the mechanic’s job has evolved from mechanical to electronic technology. Because vehicles today posses complex computer and electronic systems, mechanics need to have a broader base of knowledge than in the past. Lately, the term “auto mechanic” is being used less and less frequently and is being replaced by the euphemistic title “automotive service technician”. Fading quickly is the day of the 'shade tree mechanic', who needed little knowledge of today's computerized systems.

Due to the increasingly labyrinthine nature of the technology that is now incorporated into automobiles, most automobile dealerships now provide sophisticated diagnostic computers to each technician, without which they would be unable to diagnose or repair a multitude of common failures.