An interpersonal relationship is a strong, deep, or close association or acquaintance between two or more people that may range in duration from brief to enduring. This association may be based on inference, love, solidarity, regular business interactions, or some other type of social commitment. Interpersonal relationships are formed in the context of social, cultural and other influences. The context can vary from family or kinship relations, friendship, marriage, relations with associates, work, clubs, neighborhoods, and places of worship. They may be regulated by law, custom, or mutual agreement, and are the basis of social groups and society as a whole.
The study of interpersonal relationships involves several branches of the social sciences, including such disciplines as sociology, communication studies, psychology, anthropology, and social work. Interpersonal skills are vital when trying to develop a relationship with another person. The scientific study of relationships evolved during the 1990s and came to be referred to as 'relationship science', which distinguishes itself from anecdotal evidence or pseudo-experts by basing conclusions on data and objective analysis. Interpersonal ties are also a subject in mathematical sociology.
Romantic relationships have been defined in countless ways, by writers, philosophers, religions, scientists, and in the modern day, relationship counselors. Two popular definitions of love are Sternberg’s Triangular Theory of Love and Fisher’s theory of love. Steinberg defines love in terms of intimacy, passion, and commitment, which he claims exist in varying levels in different romantic relationships. Fisher defines love as composed of three stages, attraction, romantic love, and attachment. Romantic relationships may exist between two people of any gender, or among a group of people (see polyamory).