Self-defense or private defense is a countermeasure that involves defending oneself, one’s property, or the well-being of another from harm. The use of the right of self-defense as a legal justification for the use of force in times of danger is available in many jurisdictions, but the interpretation varies widely.
Physical self defense is the use of physical force to counter an immediate threat of violence. Such force can be either armed or unarmed. In either case, the chances of success depend on a large number of parameters, related to the severity of the threat on one hand, but also on the mental and physical preparedness of the defender.
Many styles of martial arts are practiced for self-defense or include self-defense techniques. Some styles train primarily for self-defense, while other martial/Combat sports can be effectively applied for self-defense. Not all Martial Arts are sport, so they focus their art on self defense. To provide more practical self-defense, many modern day martial arts schools now use a combination of martial arts styles and techniques, and will often customize self-defense training to suit the participants’ lifestyles, occupations, age groups and gender, and physical and mental capabilities.
Firearm, knife, tactical flashlight, tactical pen, pepper spray, stun gun, or a small impact weapon can all be used as defensive weapons.
In some countries, it is legal to use or carry weapons (for example knives, firearms or batons) for purposes of self-defense. In other countries, this may be illegal or may require a license, or some items may be legal to carry without a license, while others, most commonly firearms, are not. Limitations on the use of weapons for personal defense are a source of controversy in some countries, pitting self-defense rights against efforts to combat violent crime via restricting access to common weapons.
Everyday objects, such as baseball bats or aerosol spray cans, can also be used as improvised weapons for self-defense, but are not likely to be as effective as purpose built weapons. Some non-lethal weapons as the Kubotan have also been built to resemble everyday objects, such as keychains.
Pepper spray and personal stun guns are non-lethal self defense alternatives, which are legal in some countries. Pepper sprays can have a range between 5–23 feet, and act by delivering a spray, foam, gel or liquid containing highly irritating chemicals which causes pain to the eyes, sneezing, and sometimes temporary blindness. An example of a small disposable unit is the PepperBlaster II by Kimber Manufacturing. It uses Piexon pyrotechnic technology to propel an irritating liquid and has a three year shelf life. The Piexon JPX Jet Protector is a larger reloadable unit with a range of 23 feet. Handheld stun guns operate by delivering an incapacitating electric shock, and must actually come in contact with the assailant to be effective, with the exception of Tasers which use gas-propelled barbs connected to the taser by conductive wire to deliver the shock.
Legal in most countries are water-based self-defense sprays that contain dyes and/or marker DNA. If an attacker is sprayed in the face he will be temporarily blinded by the foam. The dye is difficult to wash-off and will stay on the skin for several days. If it is visibly removed it will still light up under UV light or leave a unique DNA trace linking the suspect to the crime scene. 
 Other forms
Being aware of and avoiding potentially dangerous situations is an emphasis of self defense. Attackers are typically larger, stronger, and are often armed or have an accomplice. These factors make fighting to defeat the attacker unlikely to succeed. When avoidance is impossible, one often has a better chance at fighting to escape, such methods maybe referred to as ‘break away’ techniques.
Verbal Self Defense aka ‘Verbal Judo’ is defined as using one’s words to prevent, de-escalate, or end an attempted assault. It is a way of using words as weapons. This kind of ‘conflict management’ is the use of voice, tone, and body language to calm a potentially violent situation before violence actually ensues. This often involves techniques such as taking a time-out, and deflecting the conversation to individuals in the group who are less passionately involved.
- Author Katy Mattingly defines verbal self-defense as simply saying no to someone or repeatedly refusing a request or telling someone who has violated a boundary what you want, or it could entail a more complicated scenario in which you are called on to refuse to engage verbally with someone manipulative, to set limits, and end the conversation.
- Suzette Haden Elgin the author of The Gentle Art of Verbal Self-Defense states that verbal self-defense defends against the eight most common types of verbal violence, and redirects and defuses potential verbal confrontations.
 Personal alarms
Personal alarms are a way to practice passive self defense. A personal alarm is a small, hand-held device that emits strong, loud, high pitched sounds to deter attackers because the noise will draw the attention of passersby. Child alarms often function as locators or device alarms such as triggering an alert when a swimming pool is in use to help prevent dangerous situations in addition to being a deterrent against would-be aggressors.[unreliable source?]
 Self-defense education
Self-defense techniques and recommended behavior under the threat of violence is systematically taught in self-defense classes. Commercial self-defense education is part of the martial arts industry in the wider sense, and many martial arts instructors also give self-defense classes. While all martial arts training can be argued to have some self-defense applications, self-defense courses are marketed explicitly as being oriented towards effectiveness and optimized towards situations as they occur in the real world. It should not be presumed however that sport based systems are inadequate, as the training methods employed regularly produce well conditioned fighters experienced in full contact fighting. There are a large number of systems taught commercially, many tailored to the needs of specific target audiences (e.g. defense against attempted rape for women). Notable systems taught commercially include:
- civilian versions modern military combatives, such as kapap, Krav Maga and Systema
- self-defense oriented forms of jujitsu, such as Bartitsu and Kodokan Goshin Jutsu.
- rape prevention, including Rape Aggression Defense System (RAD), AWARE,, Model Mugging, etc.
- Reality-Based Self-Defense (RBSD), Defensive Tactics.
- Sport based systems, such as Karate, Muay Thai, Boxing, Judo, BJJ, and Wrestling.
 Legal aspects
The most crucial difference between self-defense training for civilian application in a society under rule of law to military combatives is the necessity to consider the extent of force permitted in a given situation under the self-defense laws of the applicable jurisdiction.
The self-defense laws of modern legislation build on the Roman Law principle of dominium where any attack on the members of the family or the property it owned was a personal attack on the pater familias. In Leviathan (1651), Hobbes argues that although some may be stronger or more intelligent than others in their natural state, none are so strong as to be beyond a fear of violent death, which justifies self-defense as the highest necessity. In his 1918 speech Politik als Beruf (Politics as a Vocation), Max Weber defined a state as an authority claiming the monopoly on the legitimate use of force within defined territorial boundaries. Modern libertarianism characterizes the majority of laws as intrusive to personal autonomy and, in particular, argues that the right of self-defense from coercion (including violence) is a fundamental human right. In this context, note that Article 12 Universal Declaration of Human Rights states:
- No one shall be subjected to arbitrary interference with his privacy, family, home or correspondence, nor to attacks upon his honour and reputation. Everyone has the right to the protection of the law against such interference or attacks.
Combined with the principle of the state’s monopoly of legitimate force, this means that those authorized by the state to defend the law (in practice, the police) are charged with the use of necessary force to protect such rights. The right to self-defense is limited to situations where the immediate threat of violence cannot be prevented by those authorized to do so (in practice, because no police force is present at the moment of the threat). The right to self-defense granted by law to the private citizen is strictly limited. Use of force that goes beyond what is necessary to dispel the immediate threat of violence is known as excessive self-defense (also self-defense with excessive force, excessive self-defense). The civil law systems have a theory of “abuse of right” to explain denial of justification in such cases. Thus, in English law, the general common law principle is stated in Beckford v R (1988) 1 AC 130:
- “A defendant is entitled to use reasonable force to protect himself, others for whom he is responsible and his property. It must be reasonable.”
Similar clauses are found in the legislation throughout the western world. They derive historically from article 6 of the French Penal Code of 1791, which ruled that “manslaughter is legitimate if it is indispensably dictated by the present necessity of legitimate defense of oneself or others”. The modern French penal code further specifies that excessive self-defense is punishable due to “disproportion between the means of defense used and the gravity of the attack” defended against.
The evaluation of whether use of force was excessive in a given case can be a difficult task. The British Law Commission Report on Partial Defences to Murder (2004) Part 4 (pp78/86) recommends a redefinition of provocation to cover situations where a person acts lethally out of fear. This reflects the present view of psychiatrists that most people act in violent situations with a combination of fear and anger in their minds, and to separate these two types of affect is not legally constructive. In practice, self-defense laws still do make this distinction. German criminal law (§ 33) distinguishes “asthenic affect” (fear) from “sthenic affect” (anger). Excessive self-defense out of asthenic affect is not punishable. Outside of the western world, justifiable self-defense tends to be interpreted more loosely, including the right to defend against any criminal act, without limitations to reasonable or proportionate use of force based on the magnitude of the crime. Instead, it may simply be the minimum amount of force required to stop the criminal, which may be lethal even for relatively small crimes. Thus, the Intermediate People’s Court of Foshan, People’s Republic of China in a 2009 case ruled as justifiable self-defense the killing of a robber who was trying to escape, because “the robbery was still in progress” at this time.[18