Homophily (i.e., "love of the same") is the tendency of individuals to associate and bond with similar others. The presence of homophily has been discovered in a vast array of network studies. Within their extensive review paper, sociologists McPherson, Smith-Lovin and Cook (2001) cite over one hundred studies that have observed homophily in some form or another. These include age, gender, class, organizational role, and so forth.
In their original formulation of homophily, Lazarsfeld and Merton (1954) distinguished between status homophily and value homophily. Status homophily means that individuals with similar social status characteristics are more likely to associate with each other than by chance. By contrast, value homophily refers to a tendency to associate with others who think in similar ways, regardless of differences in status.
This is often expressed in the adage "Birds of a feather flock together".
To test the relevance of homophily researchers have distinguished between baseline homophily and inbreeding homophily. The former is simply the amount of homophily that would be expected by chance and the second is the amount of homophily over and above this expected value.
Individuals in homophilic relationships share common characteristics (beliefs, values, education, etc.) that make communication and relationship formation easier. Homophily often leads to homogamy (marriage to people with similar characteristics).
The opposite of homophily is heterophily.