The need to be and feel safe is a fundamental human need. Despite extensive theoretical arguments on the subject, and research on relevant concepts, empirical work on what it means to feel interpersonally safe (i.e., in the presence of others or in social environments in general) is scarce. This dissertation presents four investigations that seek to address this gap. It also seeks to highlight the consequences of feeling interpersonally safe for our mental and physical health, and to what degree healthy and high-quality close relationships influence how safe we feel. Chapter 1 is a literature review summarizing theories underlying these investigations and distinguishes subjective from objective safety. Chapter 2 validates a novel, comprehensive and multidimensional scale that captures perceived interpersonal safety. Chapter 3 examines the consequences of feeling safe for our mental and physical health across three developmental stages (adolescence, emerging adulthood, adulthood). Chapter 4 examines how secure attachment relates to increased feelings of safety. Chapter 5 investigates whether high-quality romantic relationships can increase overall perceptions of interpersonal safety. Finally, Chapter 6 concludes by highlighting the empirical, applied and theoretical contribution of the aforementioned investigations, concluding by posing suggestions for future research.