The book provides a foundation for categorizing the diversity of theoretical understandings and practical designs of personnel development, while also creating transparency regarding the approaches to personnel development and the underlying human models. To achieve this, the book connects insights and impulses from science with real case studies from the contexts of schools and non-profits. Personnel development relies heavily on the individuals who feel "called" to this topic and who are responsible for shaping personnel development within an organization. To support the development of employees, the book offers a diagnostic tool for daily leadership work, which contributes to the establishment of a practically relevant concept of personnel development. This concept is oriented towards the levels of personnel design.