This paper conducts a systematic literature review on knowledge management (KM) in the context of startups in order to analyze the state of the art, identify research gaps and define a future research agenda. The main findings highlight that, even though there is an increasing number of papers on the topic of KM in startups, several issues are still neglected. Specifically, the paper identifies four main gaps in the body of literature. The first gap deals with the environmental and socio-political factors influencing the adoption of KM in startups. The second gap regards the lack of a comprehensive taxonomy of knowledge management systems (KMSs) that may support the processes of knowledge creation, acquisition, storage, transfer, sharing and application. This second gap allows us to identify a third gap concerning the level of alignment between startup's strategies and technologies adopted. Finally, the fourth gap deals with the issue of the impact of KM on startup's performances with regard to economic, financial, market, technical, technological, organizational, human and relational performance. From these four gaps, six research questions (RQs) have been proposed. These RQs allow us to identify possible areas of analysis to define a future research agenda. Neglecting these issues means underestimating all the possible advantages of KM adoption for a startup to achieve efficiency, effectiveness and scalability goals.