As a concept stemming from practice, business development has received scarce academic attention. In this paper, we explore core business development activities of micro-firms and the challenges they perceive in conducting them. Based on interviews with 30 micro-firms, we identify three core business development activities that leverage the firm’s resource base, complemented by three support activities that secure and organize the firm’s resources. We find the business development activities to be tightly related to the three practices of leveraging, securing and organizing resources. We also identify three important contextual influences on business development in micro-firms: industry, age and if the firm is in an incubator. Our findings contribute to developing a conceptualization and theorization of business development for micro-firms, which is relevant as the vast majority of companies worldwide are micro-firms, but many never embark on a growth path. Based on our results, we outline practical implications, for example, how companies could overcome their perceived lack of time and an agenda for future research encouraging further studies comprising micro-firms with different qualities.