This psychobiography on the life of Karen Horney is an exploratory-descriptive study that aims to explore and describe Horney's life structure development according to Daniel Levinson's (1996) theory of adult development. The method of research uses a qualitative single-case research design that studies her life over her entire lifespan and highlights the individual characteristics of Horney in a holistic manner within her socio-historical context. A purposive sampling procedure was used to select Karen Horney as the subject of the research and only published data was analyzed in the research. Multiple sources of data are used to obtain the information in this research, including an autobiography and three biographies written by three different authors. This data is organized according to the temporal sequence of her lifespan and the developmental periods and time frame of Levinson's theory. Horney's life is described and explored to highlight those areas of her life that conform to the developmental theory and those aspects of her life that are not included in the theoretical constructs of Levinson 's theory. By exploring the significant relationships that Horney developed throughout her life with family, friends, work colleagues, community and religious affiliations, and the important issues in her development, this study verifies Levinson's theory by corroborating his conceptualisation of adult development as a process of sequential stages divided into four main eras of development, linked by three periods of transition. A shortcoming of Levinson's theory relates to his omission of self-esteem issues and religious concerns as relevant factors experienced during the era of pre-adulthood and spiritual concerns during the era of late adulthood.