The study analyzes the sources of informality in land transactions, emphasizing the inefficient nature of land markets. Although previous works articulate the concept of informality around a deviation from the rules by economic agents, the approach adopted here is that of a deviation reinforced by the imperfection of land markets. This perspective is in line with the New Microeconomics, which argues that violation of the assumptions of the standard neoclassical model, such as perfect information and complete markets, is a source of misallocation. In line with the New Institutional Economics (NIE), the informality of land transactions is based on the existence of transaction costs. From this theoretical framework and based on data collected in the city of Douala, we analyze the impact of the lack of information, the increased presence of transaction costs and the incompleteness of the land market on the occurrence of informal land transactions. A two-stage probit estimation yields the following results: i) the lack of land information and the dominance of informal information channels significantly increase the risk of land informality; ii) the increased presence of transaction costs is a factor that significantly aggravates the risks of informal land transactions; iii) the absence of price offers adapted to the underprivileged is also a significant catalyst of land transaction informality. These results suggest three policy directions. First, the establishment of a systematic and universally accessible land information platform is desirable. Second, it is desirable to control transaction costs. Two levers can be used for this purpose: a) reducing the number of procedures for issuing land titles, as these are tainted by rents; b) reducing notary fees, which increase the cost of signing. Thirdly, it is desirable to envisage land reserves specifically dedicated to vulnerable groups.