Over the last three decades, the scientific and social interest in workplace bullying has accelerated and our understanding of this pervasive and detrimental social problem has advanced considerably in a relatively short amount of time. Workplace bullying is now a phenomenon of global interest, new topics are steadily emerging within the field, and the methodological quality of the studies has become more sophisticated. Building on findings from the ever increasing number of systematic reviews and meta-analyses in this field, the aim of this literature overview was two-folded. In the first part, the aim was to provide a basic overview of what we already know with regard to the nature and content of the bullying phenomenon, its risk-factors and causes, its consequences, and its potential measures and interventions. In the second part, the aim was to address what we do not know and to put forward an agenda for future research within the field. Here, six major knowledge challenges are discussed: a) construct clarification, b) the need for theoretical models, c) causality, d) bullying as a process, e) mediators and moderators, and f) intervention and rehabilitation of victims, perpetrators, and work environments.