There are two ways to answer this question. First there is the actual legal theory you'll sue for -- the legal argument you will use to try to hold the defendant liable (this is called a "cause of action" in legalese). And second, there is the dollar amount you will sue for -- in other words, the “damages” you will ask for as part of the lawsuit. Let’s look at these issues separately.
The cause of action you’ll usually sue for in a car accident case is called “negligence,” which is a legal concept that forms the basis of most personal injury lawsuits. In a nutshell, negligence can be defined as the failure to exercise a reasonable level of care considering the circumstances. So, in the context of a car accident claim, when Driver A’s failure to use reasonable care ends up causing harm to Driver B, then Driver B can file a lawsuit alleging that Driver A was negligent. The violation of a traffic law can amount to negligence when it causes an accident, as can texting while driving, failure to keep a safe following distance, and any number of other careless and dangerous driver behaviors.
To learn more about different liability issues in a car accident case, see Proving Fault for a Car Accident.
The amount of money you’ll sue for in a car accident case is determined by what you’ve lost, both monetarily and otherwise. That includes medical expenses to treat injuries stemming from the accident, the cost to repair vehicle damage (or to replace your vehicle if it’s deemed a total loss), reimbursement for time missed at work and any other lost income, compensation for pain and suffering and other negative effects of the accident. To find out more about how much you should ask for in your lawsuit, check out How Much is My Car Accident Claim Worth?