Public-private partnerships (PPPs) have motivated diverse bibliometric analyses of PPP research. Nevertheless, the evolution and connections between the main topics in the PPP domain have not been explored. To improve the understanding of the PPP research agenda, this study uses Content Analysis (CA) and Semantic Network Analysis (SNA) to expose relationships and trends in PPP research topics over the last two decades. These methodologies helped researchers to move beyond analyzing thematic trends in isolation in order to gain insight into the interrelationships among PPP topics by using qualitative and quantitative tools, which is difficult to achieve with other methodological approaches. The SNA metrics showed that the PPP research agenda evolved into a high-clustered network driven by five macrokeywords: financing and economic aspects, road infrastructure, public sector management, risk management, and contract management. These macrokeywords may enable the growth of the entire PPP research agenda, but they could also jeopardize the emergence of new research trends. Results show that the participation of some traditional PPP infrastructure types, such as power generation, rail, and tunnel, has been reduced, in contrast to more recent types such as healthcare and, especially, airport infrastructure. Similarly, research focus has shifted from examining traditional PPP issues in the US and European Union to analyzing PPP development in Africa, Latin America, and Asia. Overall, this study presents a more holistic understanding of the PPP body of knowledge, its evolution, and the interaction of its main topics.