Humans are radically interconnected, not just isolated individuals. Their self-concepts can reflect this by expanding in space-time beyond contemporary Western understandings of people as separate, bound within their skins in the present. Instead, humans can self-identify more expansively with external others and nature, their internal organs and cells, and aspects of their past and possible future existence. However, self-identifications can go much further through including all of humanity, all of life, and even all that exists as being within one's self-concept. These extreme identifications can be seen as transpersonal, namely by expanding (“trans”) the conventional limits of how a person is usually viewed. Sometimes these extreme identifications might even be considered spiritual, but that term unfortunately invokes the metaphysical divide of “spirit” pitted against nature. In contrast, transpersonal psychology can provide a thoroughly naturalistic and scientific way to deal with extreme interconnectedness that avoids such undue metaphysical speculations. This is especially useful when addressing frontier topics, such as higher consciousness and deeper meaning, and offers ways to integrate many conventional psychological approaches under more inclusive frameworks that remain scientific. The construct of self-expansiveness, as one transpersonal approach, provides a way to understand and measure self-concept that incorporates transpersonal identifications with the same scientific rigor found in conventional approaches. This offers avenues for exploring holistic solutions for the optimum development of human potential, as well as for reconciling vexing dilemmas that stem from narrowly isolated, rather than expansively interconnected, self-concepts, such as conflicts among humans and between humans and their environment.