Complementarity refers to ways a couple provides what each other needs in a relationship i.e. they complement each other
Complementarity forms the third level of filtering
A couple who complement each other will each bring to the relationship something that their partner is not able to bring
Complementarity, according to Kerckhoff & Davis (1962), is not so important in the early stages of a relationship but is crucial for long-term happiness
A successful relationship depend on complementarity as each person fulfills the needs of their partner which results in a relationship that does not consist of two separate individuals but is instead a whole