This final chapter will sketch out a few of the thoughts and considerations prompted by a reading of the contributions in this volume. The book's intention was to cover the whole spectrum of relationships experienced by people in everyday life, and the following remarks refer to questions and problems arising from this spectrum. The questions are not new, nor are any solutions offered to the problems addressed here. But it appears useful for an appropriate assessment of existing results and the future tasks of relationship research to address these questions and problems not just once but time and again.

The complete catalogue of interpersonal relationships?

In view of the broad spectrum of interpersonal relationships treated in this volume, it is tempting to consider whether some important types of relationship have been neglected. Apart from the fact that some readers may be surprised to discover that marital relationships have not received an independent chapter, it appears that most relevant interpersonal relationships, at least those in our cultural and historical context, have been addressed: parent–child relationships, peer and sibling relationships during childhood, relationships between adult siblings, child–parent relationships in adulthood, different types of relationships in families and among relatives, friendships, heterosexual and homosexual relationships, relationships with acquaintances and neighbors, and occupation-determined relationships between colleagues, and role relationships. This extensive list could conceivably be lengthened to include thematically oriented relationships that develop when people share the same interests or aims (see also Krappmann, Chapter 2 of this volume), but this type of relationship can also be seen as a subgroup of the heterogeneous and less clearly definable category of acquaintance relationships (see also Melbeck, Chapter 11 of this volume).