A CGL responds to three kinds of harm: bodily injury, property damage, and personal and advertising injury. Most mistakes by professionals cause none of these. When a CPA misses a filing deadline and the client owes extra tax penalties, nobody is hurt, nothing is damaged and nobody is defamed. The loss is purely financial, so the claim never even reaches the CGL's exclusions.

Some professional mistakes do cause bodily injury or property damage, and they can still fall outside the CGL because an exclusion applies. Engineers, architects and similar firms commonly have a professional services exclusion endorsement on their CGL. If an engineer's design error makes a roof collapse, the injuries and damaged stock meet the CGL insuring agreement but are excluded, so the claim goes to the professional liability policy.

Who buys it: people who give specialized advice or services, such as physicians, attorneys, accountants, architects, engineers and insurance agents. For medical professionals it is usually called malpractice insurance; for others it is errors and omissions (E&O) insurance. A shoe store has premises and products exposures, which a CGL or businessowners policy handles.

What it covers that a CGL does not: harm from negligent acts, errors or omissions in rendering professional services, including a client's financial loss with no physical injury. A client's lost revenue from a consultant's negligent business advice is the classic example. A customer slip, a spreading fire or libel in an ad remain CGL exposures.