The term interpersonal attraction in Psychology is defined as:

1. An Attraction between people which drives them to fall in love and form a long-term romantic relationship.

2. An individual’s desire to establish a friendly or romantic relationship with another individual.

3. A person’s positive attitude towards (or positive evaluation of) a particular person. Like any other attitude, this attitude has also three components:  1) cognitive (perception of a person as good or beautiful), 2) affective (feeling of liking towards the person), and 3) behavioral (tendency to approach the person).

Interpersonal attraction is one of the socio-psychological needs of human beings. Since human beings have an inborn instinct for sociability, they generally enjoy the company of others. For this reason, some psychologists view extreme introvertial tendency as an abnormality. Linked with this general tendency, human beings also desire to have someone personally close to them, with whom they can share their personal emotions and ideas to get psychological gratification. This desire to have someone close to them to seek psychological gratification leads to interpersonal attraction – to be attracted to someone who is viewed as suitable (for a friendly or romantic relationship).

Everyone wants a companion to live life with because such a healthy relationship enables one to lead a happy life. This is an important aspect of life because it brings psychological stability to people in the relationship because it satisfies an individual’s psychological curiosities and needs in relation to the gender that an individual is attracted to. Without this need and curiosity satisfaction, an individual may experience varying degrees of internal psychological instability, which may or may not come into visible expression. This is why an individual is attracted to or fall in love with another individual.

Attraction towards a person is based on the perceived suitability of the person for a close relationship which can be explained in terms of the following factors of interpersonal attraction. This explains the psychology of falling in love with a particular person. 

It is natural to attract to what appeals. Therefore, appearance and physical characteristics have a major role in getting attracted to a person. In other words, beauty (or perceived beauty to be more correct) attracts. The definition of beauty varies from person to person. One person may view someone as beautiful who may not be viewed as beautiful by another person. However, some characteristics may typically be viewed as an indicator of beauty. For instance, men may be attracted to women that have big eyes, fair complexion, thin eyebrows, prominent cheekbones and so on. Women may find tall and muscular men more attractive.

Generally, people have an image of idealized beauty in their mind which also serves as a basis for the appearance of their dream person. Whenever they come across a person which fits into the image of their idealized beauty (as in their mind), they fall in love with the person.

It is also a psychological tendency that people generally perceive a beautiful person to be also a good, loving, and caring person and like a person who treats others well. This is another reason why people may get attracted to a person with a good appearance.

It is not only appearance but also personality characteristics that attract. In some cases, the personality characteristics may even bypass the role of appearance in making someone fall in love. For instance, one person may fall in love with another person not because that the person perceives the other person as beautiful but solely because of the impressive personality characteristics of the other person. However, it is also true that when personality characteristics are attractive enough to fall someone in love, the person is also perceived as beautiful by the lover.

Every person has different personality characteristics such as jovialness or seriousness, aggressiveness or calmness, the way the person thinks and acts, the way the person talks to others, the way the person treats others and so on. The attraction to personality characteristics is mostly based on one’s own personality characteristics. For instance, a jovial person would be more attracted to a jovial person than to a serious person. Similarly, a serious would be more attracted to a serious person and would feel irritated from an overly jovial person. Attraction to personality characteristics (such as the way individual talk to other or treat others) of a person depends how much these characteristics matter for (or valued by) the other person in general.

Every person has specific interests, beliefs, and attitudes. An individual is more likely to be attracted towards another individual who has similar interests, beliefs, and attitudes. The similarity in these areas assures mental compatibility between the two individuals going into a relationship. For instance, a person with modern and liberal preferences may find it a bit difficult to adjust with a person with conservative and orthodox preferences. On the other hand, if the individuals have similar interests, beliefs, and attitudes, it provides validation of their choices and ideas.

Similarity factor also applies to socio-demographic characteristics (e.g., age, social class, educational attainment) and cultural characteristics (e.g., cultural values and beliefs, language). Generally, people get attracted to others of similar age, social class, educational attainment. The similarity in cultural characteristics is sometimes viewed as more important because the individuals feel secure and not threatened by those having common cultural beliefs and values. 

Similarity factors sometimes also applies to the appearance of a person. Some people may prefer others that are roughly equal to them because doing so may help them not face an inferiority complex.

The similarity is generally viewed as important for a happy and joyous relationship. If the spouses are different in many respects, they feel difficult to adjust with each other and have to compromise on many of their choices to save the relationship.

As discussed above, similarity leads to attraction. However, sometimes people are also attracted to others who are different from them. The reason for this is to achieve complementarity – to complement each other - where 1) both individuals think that their different characteristics would combine to complete the relationship, or 2) one individual thinks that his or her characteristics would be influenced and improved by the differing characteristics of another person.

For instance, an individual finds the other individual to be more exciting because the individual thinks it would have a good impact on their relationship as well as on the mood of the individual himself or herself who lacks excitement. Likewise, an individual may be attracted to the other individual who has better socio-economic status because the individual thinks it would have good outcomes for their overall relationship as well as for the individual himself or herself who has lower socio-economic status. Since complementarity attraction is based on the difference in characteristics, it usually does not last long like the attraction based on similarity. Likewise, an attraction based on similarity is generally more intense than attraction based on the difference in characteristics.

The term reciprocity means to respond to others in the same way they acted towards you. Interpersonal attraction is also sometimes a product of reciprocity. It means that when we come to know that someone loves us, it causes us to love that person too. This happens because when people come to know that they are loved by someone, they feel of themselves as valued and respected by the person which may naturally trigger their feeling of liking towards that person. Similarly, when you come to know that someone loves you, you feel that that person shows regard to you and your characteristics, you enjoy this feeling and get attracted to that person to continue enjoying this feeling.

Propinquity effect means that people who live near each other or frequently meet each other have more tendency to form a friendship and romantic relationship. The reason, why people are more attracted to those who are near to them, is that they have more chances to meet each other, talk to each other, know each other, and are easily influenced by each other. Likewise, it is natural that when we meet someone frequently, we slowly and gradually start liking them. Another reason is geographical proximity that means it is easy to form a relationship with those who are near (accessible) to us compared to distant ones. For this reason, interpersonal attraction may sometimes be seen in people working in the same workplace or studying in the same institution.

Physical distance is an important factor; however, nowadays social media and the internet have made communication very easy and the people living far away from one another may also get attracted to one another.